Entry No. 7 — the Denver file — filed under: street art
RUMTUM UV-Reactive Mural
RiNo is wall-to-wall murals, but this RUMTUM piece has a second painting hiding inside it that daylight never shows. The artist worked UV-reactive elements into the design, so the concealed imagery only appears after dark under a blacklight, and basically nobody walks the murals carrying one. Show up at night with a cheap UV flashlight and the wall changes into something else entirely. It lives on a quieter stretch of Walnut, in the alley between 28th and 29th.
The story
Denver's River North Art District has thousands of square feet of outdoor paint, but almost every inch of it plays by daylight rules. Artist RUMTUM—the moniker of Denver muralist, printmaker, and musician John Hastings—quietly inverted that dynamic on a semi-industrial stretch of Walnut Street. To a casual daytime passerby, the wall looks like one of his standard organic, graphic landscapes. But Hastings worked invisible ultraviolet pigments directly into the paint, baking a second, hidden layer of imagery into the brickwork that remains invisible until hit with blacklight wavelengths.
Because virtually nobody walks Denver's side streets carrying a blacklight beam, the secret imagery lives in plain sight, completely ignored by the crowds streaming along nearby Larimer. You have to hunt down the alley running between 28th and 29th Streets, step off the lit sidewalk, and bring your own hardware-store UV flashlight. When the blue-violet light hits the wall, invisible glowing shapes and linework flush into view—a secret ghost image floating over the daytime paint.
The catch is catching it before it vanishes. RiNo's walls are notoriously volatile, constantly prepped, primed, and buffed for annual street art festivals or private development. That impermanence is part of the deal: this isn't a museum piece behind protective glass, but an unsanctioned-feeling outdoor secret living on an alley wall tucked between working bays and residential properties.
What it's like
Arrive after sunset when the ambient light drops. Park along Walnut Street or use one of the district's paid lots, then cut into the alley behind 28th and 29th near the 2555 Walnut block. The alley backs onto active residential and working properties, so keep your voice down and kill bright phone flashlights before firing up your pocket UV light. You won't find signposts, velvet ropes, or crowds—just quiet brickwork that abruptly shifts into a glowing neon secret under blacklight. Verify local mural maps before trekking out, as RiNo walls are routinely painted over without warning.
The move: Bring a small blacklight/UV flashlight and go after dark: walk the Walnut alley, find the RUMTUM wall, then kill the phone lights and watch the hidden imagery glow into view together.
📍 Before you go This sits on a quieter, semi-industrial stretch of Walnut at the edge of RiNo's denser mural core, so plan to park on the street or in one of the district's paid lots and walk the last few blocks in. RiNo is Denver's thickest concentration of murals, so build a broader wall-crawl around the visit and cap the evening at a Larimer-corridor brewery or eatery a short walk away. One real catch: these walls rotate, especially after the district's late-summer-into-fall mural festivals, so confirm this specific piece is still up before making a special trip. The alley backs onto working and residential property, so keep the noise down and be respectful late at night.
- 📍 RiNo (River North Art District)
- 💸 Free
- ⚡ Low-key
- 🌗 Outdoors
Where: RUMTUM mural, Walnut St alley between 28th and 29th, Denver (RiNo); near the 2555 Walnut St vicinity
Hours: Outdoor public mural, accessible anytime, but the hidden UV effect only works after dark, so go at night and bring your own blacklight. Murals can be repainted over time.
Pair it with
- One River North (MAD Architects canyon floors) — Follow a night of blacklight alley-crawling with a stroll past this 16-story apartment block torn open by a planted, four-story open-air canyon.
- Dateline Gallery — Pair this hidden outdoor wall with RiNo's quintessential underground gallery space that stays anchored to the neighborhood's original, pre-gentrification DIY roots.
- Cat Alley (Alley Cats by Kelly Monico) — Extend your alley-hunting habit across town to LoDo, where three hundred cast feline figurines hide in plain sight between 14th and 15th.
Good to know
What kind of flashlight do I need to see the hidden art?
A cheap 395nm or 365nm UV LED flashlight works best; standard smartphone lights and white-light flashlights will not activate the ultraviolet pigments.
Where exactly is the mural located?
It sits on the Walnut Street alley wall between 28th and 29th Streets in RiNo, around the 2555 Walnut Street vicinity.
Is there an admission fee or set hours?
No, it is a free, self-guided public mural accessible 24/7 on an outdoor alley wall, though the hidden imagery can only be viewed after dark.
Is the mural guaranteed to still be there?
RiNo walls rotate frequently due to annual mural festivals and property repainting, so check local street art maps or artist feeds to verify it hasn't been painted over before heading out.
Plan a visit & invite your people →
Further reading: rinoartdistrict.org · denversam.com
last checked: 2026-06-07