What is "zoobomb"

Zoobomb is a weekly bicycling activity in Portland, Oregon, United States during which participants ride bicycles rapidly downhill in the city's West Hills. Zoobomb began in 2002.

Participants carry their bikes on MAX Light Rail to the Washington Park station next to the Oregon Zoo. From there, participants take the elevator to the surface and then ride their bikes down the hills in the vicinity. This process is often repeated several times throughout the night.