Woodstock was a music festival. The Twelfth Doctor told Clara that his tambourine solo was one of the highlights of Woodstock. (PROSE: The Crawling Terror)
When on the Twist, the Twelfth Doctor mentioned Woodstock while talking about open-air concerts. (COMIC: The Twist)
The Seventh Doctor once speculated that there would be at least two versions of himself at Woodstock. (PROSE:The Left-Handed Hummingbird)