4 days by RV from Denver: Bishop Castle, the UFO Watchtower and Great Sand Dunes

The valley floor is so flat and so high that the sky seems to start at your feet. To the east, a wall of mountains over 14,000 feet; at their foot, the tallest sand dunes in North America. On the other side of the valley, beside the highway, a man-made platform with a sign that invites you to watch for UFOs. On the way in, a stone castle built by one man in the forest. This is the San Luis Valley in southern Colorado.

This is a four-day RV loop from Denver: Bishop Castle, the UFO Watchtower near Hooper, and Great Sand Dunes National Park, with a night under some of the darkest skies in the West. It's a different trip from our 6-day Rocky Mountain itinerary: south instead of north-west, sand instead of tundra. We tell the UFO stories the way the places themselves tell them, and we label them: we never claim that UFOs, alien visits or "energy" spots are real. Every price, opening hour and RV rule below comes from the operator or a public agency, with the date we checked it. Anything we estimated is marked [A].

When to go

1. JanToughAlamosa lows −1 °F
2. FebToughlows 7 °F
3. MarToughpark campground closed
4. AprGoodcold nights, creek starts
5. MayBestcreek peak late May
6. JunBestcreek, then mosquitoes
7. JulGoodhot sand, storms
8. AugGoodhot sand, storms
9. SepBestmild days
10. OctGoodlows 25 °F
11. NovToughlows 12 °F
12. DecToughlows 1 °F

Our rating [A], based on NOAA 1991–2020 normals for Alamosa: highs of 80–83 °F in June and July, but lows of about −1 °F in January and 25 °F even in April and October [V23]. The valley is high; at night, RV water lines can freeze outside summer [A]. Medano Creek, the shallow creek at the foot of the dunes, usually flows from April, peaks in late May and early June, and is mostly dry at the main area by July [V10]. Bishop Castle sits at about 9,000 feet [V6], and CO-165 and La Veta Pass can have snow and ice from October to April [A]: check cotrip.org before you drive.

Route map

The 4 days at a glance

swipe sideways to see the whole table →

Distances and drive times are our estimates for an RV at legal speeds without stops, from a road router [A]. Add 20–30% for photo stops, Denver traffic and mountain grades. Day 4 is long: check your RV return time before you book, or add a night (see alternatives).

Before you go: checklist

1. Book Piñon Flats Campground in Great Sand Dunes National Park for night 3, on recreation.gov or by phone (1-877-444-6777). All sites are by reservation, up to 3 months ahead; it's open April through October [V11][V12]. $20 a night [V11]. No hookups, no showers [V12]. Most sites take tents and RVs up to 25 ft; only eight sites (8, 39, 47, 60, 76, 77, 80 and 86) fit 35 ft, the total limit for RV plus anything towed [V11][V12].
2. No luck in the park? The Great Sand Dunes Oasis, just outside the entrance, has 20 pull-through full-hookup sites (30/50 amp) at $55 a night for two people. Book by phone, 719-378-2222, at least 48 hours ahead [V15].
3. Book Lathrop State Park near Walsenburg for night 1: reservation required, at cpwshop.com or 1-800-244-5613, up to six months ahead. Campsites are $28–36 a night, and you also need a daily vehicle pass ($10–15). The Piñon campground has paved sites with up to 50-amp power, and the park has a dump station, water hydrants and showers [V17].
4. Pick your night 2. The comfortable base is Alamosa: the Alamosa / Great Sand Dunes KOA Journey, 3.5 miles east of town on US-160, has pull-through sites with full or partial hookups and 50-amp power, and is open March 1 to November 14 [V16]. Cool Sunshine RV Park, in town within walking distance of downtown, also has full hookups [V14]. The adventurous option is to camp at the UFO Watchtower itself: no reservation needed, $20 a night per tent, RVs welcome without hookups; call ahead on 719-378-2296 [V1].
5. Know your RV's length. Over 35 ft, Piñon Flats is out [V12]; book the Oasis instead [V15]. Our RV size guide helps if you're unsure.
6. Plan your days of the week. In autumn and winter the Watchtower opens Friday to Monday, 10 am–4 pm, says its own website [V1]. Other listings say daily 10 am–5 pm in summer [V3]. Call before you go [A]. In late May and early June, avoid weekends at the dunes if you can: the park calls them "extremely crowded" [V10].
7. Plan your water and tanks. Piñon Flats and the Watchtower have no hookups [V11][V1]. The national park's dump station and water hoses work only "in warmer months" [V11]. Fill up and dump at Lathrop on day 2 [V17] and, if you sleep there, at the Alamosa KOA [V16].
8. Bring cash for the Watchtower and the donation box at Bishop Castle [A]; the park takes cards and phone payment [V18].

RV access, stop by stop

RV ok paved, parking for a typical campervan or Class C up to ~30 ft [A] · Caution possible, with a catch · No RV leave the RV and walk, take a car, or skip

swipe sideways to see the whole table →

Not sure your rig fits? Our RV size guide explains length, height and what "unpaved" means in a rental contract.

Where you sleep: hookups and dump stations

swipe sideways to see the whole table →

Two nights in a row without hookups (Watchtower, then Piñon Flats) is possible with full fresh water and empty tanks from Lathrop [A], but tight in a small campervan. If you're unsure, sleep in Alamosa on night 2. Sleeping in a vehicle anywhere in the national park outside a campground is not allowed [V13]. For what to do when every campground is full, see our plan B guide.

Day by day

Day 1 — Land in Denver, pick up the RV, Lathrop State Park (~183 mi)

Fly into DEN and do the RV walk-through slowly: photos of every scratch, tank levels, generator and heater test. You'll want the heater: nights in the valley are cold for most of the year [V23]. Do one big grocery and water run in Denver [A]. Then take I-25 south past Colorado Springs and Pueblo to Walsenburg, and turn west to Lathrop State Park, about 183 miles from the airport [A]. Check-in is from 1 pm [V17]. Fill the fresh-water tank here: you may not see a hookup again until night 3 [A].

Sleep: Lathrop State Park, electric site [V17].

Day 2 — Bishop Castle → La Veta Pass → Alamosa (~167 mi)

Dump and fill at Lathrop, then drive back north on I-25 to exit 74 at Colorado City and turn west onto CO-165. The castle is 24 miles up the road, on the left [V8], at just over 9,000 feet [V6]. It's a slow, winding mountain road [A]; give yourself an hour. There's no parking lot: you park along the highway shoulder [V8]. Come early, and in a big Class C, look for a long, level stretch before you stop [A].

Bishop Castle is free. A sign asks for donations, and another tells you that you're there at your own risk [V7]. Take that seriously: the towers have narrow stone stairs and open iron walkways high above the ground [A]. Children and pets are your responsibility, says the castle [V6].

Back down CO-165 to I-25, south to Walsenburg, then west on US-160 over La Veta Pass into the San Luis Valley [A]. Alamosa is about 115 miles from the castle [A]. Check in at your RV park and take it easy: you're now at about 7,500 feet [V20][A], and many visitors feel the altitude on their first night [A].

Want the night under the stars? Drive on instead: 22 miles north of Alamosa on CO-17 to the UFO Watchtower [A], arriving before 5 pm (4 pm out of summer) and after a phone call [V1]. That makes day 2 about 193 miles [A]. Read the day 3 section first: the stories, the rules and what you'll actually see are the same.

Sleep: Alamosa / Great Sand Dunes KOA Journey or Cool Sunshine RV Park, full hookups [V16][V14]; or the UFO Watchtower campground, no hookups [V1].

Day 3 — UFO Watchtower → Great Sand Dunes (~58 mi)

From Alamosa, take CO-17 north through Mosca and Hooper. The Watchtower is on the west side of the highway, a couple of miles past Hooper [V1][V3]. Ignore your GPS, follow the alien signs [V1].

The UFO Watchtower is a folk attraction, and a friendly one. Judy Messoline, who created it, says she kept hearing "Great Sand Dunes" and "San Luis Valley" on UFO television shows, and decided to build a place to watch the sky [V1]. You'll find a raised viewing platform, a garden where visitors leave small trinkets and stones, and a gift shop with alien souvenirs and visitors' sighting stories [V2]. Admission is $5 per person; under 6 free [V1]. Give it an hour [A]. Don't expect science: expect conversation, kitsch and a very big view.

The tourism listing says the garden holds "two documented energy vortexes" [V2]. We found no measurement behind that [A], and we label it as marketing.

From the Watchtower, go back south on CO-17 to Mosca, then east on County Lane 6, a paved road straight towards the dunes [V9]. That's about 33 miles [A]. Pay at the entrance station ($25 per vehicle, valid 7 days; cards and phone payment accepted) [V18], stop at the visitor center (open daily, 9 am–4:30 pm in winter, longer in summer) [V19][V20], and drive on to Piñon Flats Campground, one mile north, from 2 pm [V11].

Great Sand Dunes has the tallest dunes in North America [V20]. The two highest, Star Dune and Hidden Dune, each rise 741 feet from base to summit [V21]. They lie at the foot of the Sangre de Cristo Mountains, where opposing winds pile the sand up rather than blowing it away [V21]. In the late afternoon, walk from the Dunes Parking Lot to the top of the first ridge: about a mile in a straight line, best done in zig-zags along the ridges, and about an hour for most people [V20]. There's no trail and no shade [A]. On a summer afternoon the sand can be hotter than 150 °F, so wear closed shoes, not sandals; and when a storm comes, get off the dunes, because lightning often strikes them [V20]. When sand slides down a steep face, you may hear it hum: the "singing sands" that inspired a 1940s Bing Crosby song, "The Singing Sands of Alamosa" [V21].

After dark, stay up. Away from the campground lights, on a moonless night, the Milky Way stands over the dunes [V22]. Use a red light to keep your night vision [A]. The park has offered free night-sky programs on summer weekends [V22]; ask at the visitor center [A].

Sleep: Piñon Flats Campground, no hookups; generators only 8–10 am, noon–2 pm and 5–7 pm; quiet hours 10 pm–6 am [V11]. Or the Great Sand Dunes Oasis, full hookups [V15].

Day 4 — Great Sand Dunes → US-285 → Denver (~252 mi)

Get up early and walk on the dunes while the sand is cool and the light is low [V20][A]. Leave by about 10 am [A]. Take County Lane 6 back to Mosca and CO-17 north up the valley to US-285, then over the mountains via Poncha Springs and Fairplay to Denver [V9]. The park gives about 234 miles to Denver this way, against 242 via I-25 [V9]; to the airport it's about 252 miles [A]. US-285 climbs over several mountain passes; use low gears on the way down [A].

Return the RV: dump, refuel to the level in your contract, sweep out the sand (there will be sand) and return on time [A]. Leave at least 3 hours between the RV return and your flight [A].

Fact or folklore?

Every claim on this route, sorted. "Tourism marketing" means the claim comes from the business or tourism office itself; it may be true, but nobody independent has checked it.

swipe sideways to see the whole table →

What we left out, and why

• The Stanley Hotel in Estes Park. Known for its ghost stories, but it's north-west of Denver, the opposite direction from this valley. It belongs with a Rocky Mountain trip, not this one [A]. We haven't checked its current details, so we don't list them.
• The Medano Pass Primitive Road. High-clearance 4x4 only; all-wheel and two-wheel drive are prohibited [V10].
• Zapata Falls. A pretty BLM area 11 miles south of the park, but the access road is bumpy dirt [V14]. Not for a rental RV [A].
• GPS "shortcuts" across the valley on gravel county roads. See the GPS box.
• Paid UFO or "energy" tours. Not needed, and we don't recommend tours that sell healing or contact claims [A].
• Snippy's skeleton. It became a novelty in Alamosa, passed from owner to owner, was offered on eBay in 2006 and is reportedly in a warehouse now [V5]. There's nothing to visit [A].

Alternatives: 3 days, other way back

Buffer day: if you can, add one spare day, ideally on the first night near the airport or right after the longest drive. It absorbs a late flight, a slow pickup, a closed road or bad weather without cancelling a booked campground. Our classic loops show where it fits.

• 3 days, without the castle. Day 1: Denver → US-285 → CO-17 → UFO Watchtower, about 221 miles [A]; camp there, or sleep in Alamosa. Day 2: the dunes, night at Piñon Flats or the Oasis. Day 3: back to Denver on US-285 [A]. You skip Bishop Castle and one long interstate day.
• Other way back. From the dunes, take CO-150 south and US-160 east over La Veta Pass to I-25 at Walsenburg, then north to Denver: about 242 miles to Denver, says the park [V9]. More interstate, fewer passes [A].
• 5 days. Add a second night at the dunes: a slow morning, a longer hike, and a second chance at clear skies [A]. Piñon Flats allows it if you book both nights [V11].
• Combine with the Rocky Mountains? Do this loop first, return to Denver, then follow our 6-day Rocky Mountain itinerary, which has its own timed-entry and campground rules [A].

What it costs

Verified prices on this loop (checked 2026-10-28): Lathrop State Park $28–36 a night, plus a $10–15 daily vehicle pass [V17]; in Alamosa, the KOA doesn't publish a price, and guests reported $74–89 a night in autumn 2026 [V16]; Piñon Flats $20 a night [V11], or the Oasis $55 with full hookups [V15]. Camping at the Watchtower is $20 a night per tent [V1]. That's about $135–200 for three nights before tax [A]. Entry: Great Sand Dunes $25 per vehicle for 7 days [V18]; UFO Watchtower $5 per person [V1]; Bishop Castle free, donations welcome [V6]. An America the Beautiful pass covers the national park (non-US residents $250 a year) [V18].

The big items are the RV and fuel. At about 660 miles, a Class C that does 8–10 miles per gallon burns roughly 65–85 gallons [A]. Put your own dates, vehicle and fuel price into the trip cost calculator (choose 4 days and about 660 miles).

← All day-by-day itineraries

Affiliate note: there are no affiliate links on this site yet. Once partner links go live, they will be marked and we may earn a commission at no extra cost to you. We don't accept paid rankings. See our disclosure.