Bicycle Day is an annual, informal holiday celebrated worldwide on April 19 to commemorate a major event in the psychedelic world.
On April 19, 1943, Swiss chemist Albert Hofmann, purposefully ingested 250 micrograms of LSD. It was the world’s first intentional acid trip.
Feeling intense effects, he rode his bicycle home from his laboratory in Basel, Switzerland, a journey that has become a defining moment in psychedelic history and culture.
More info
https://en.wikipedia.org/wiki/Bicycle_Day_(psychedelic_holiday)