On April 19, also known as Bicycle Day, it makes sense that we’d be celebrating every single trip made by bike—but we want to call attention to one trip in particular.

For most people, Bicycle Day sounds like a day to revel in all things cycling. But did you know that it’s actually a day that celebrates LSD? It was this day in 1943 when Swiss chemist Albert Hofmann, the creator of LSD, decided to whip up a new batch and head out for a bike ride.

The result was a trippy bike ride through the streets of Basel, Switzerland, accompanied by his (likely very nervous and confused) assistant. According to Rolling Stone, it was—seriously—4:20 p.m. on April 19 when he decided to dose himself. The result, he realized, was that rather than experiencing any of the physical results he’d hoped for when initially creating the lysergic acid diethylamide (LSD) compound, he was—to put a fine point on it—tripping balls.

“Kaleidoscopic, fantastic images burst in upon me, alternating, variegated, opening and then closing themselves in circles and spirals, exploding in coloured fountains, rearranging and hybridizing themselves in constant flux,” he later wrote in his memoir, LSD: My Problem Child.

His six-mile ride home was a revelation in his mind, though unremarkable in terms of the route or anything that happened as he pedaled. He made it safely home, with no unfortunate side effects, just a new idea that would change how scientists would view brain chemistry going forward. The ride was also commemorated by an anonymous artist in 1993, who created perhaps the coolest image ever of a scientist on a bike. (Yes, even cooler than this Einstein one.)

According to DaysOfTheYear.com, Bicycle Day didn’t begin until the 1980s, when a professor started hosting a small-scale party that eventually grew into a worldwide phenomenon. It’s not to be confused with World Bicycle Day, a UN-recognized holiday that takes place on June 3.

A tribute to Alfred Hofmann by Banksy.

Yui Mok – PA Images//Getty Images

It’s worth noting that while Hoffman’s famous bike ride and subsequent holiday in his honor are fodder for a fun story in the cycling world, the recognition of LSD as a substance that could be used as a psychiatric tool is bigger than bicycling. His research helped develop a better understanding of the brain: The idea that mental illness cannot always be treated by psychological interventions alone, that brain chemistry plays a vital role. LSD might call to mind acid trips and hallucinations, but researchers are finding that it, along with other psychedelics, may help treat depression, PTSD, and more.

Alfred Hofmann died from a heart attack at age 102 on April 29, 2008 in Burg im Leimental, Switzerland. Whether you’re a fan of psychedelics or not, we highly encourage getting out on a bike ride today to celebrate the legend.