The Who, YouTube

The Monterey Festival was the first major rock gathering but Woodstock was definitely the largest and most famous where folks gathered in Sullivan County, New York  on a farm which actually is about 40 miles from the town of Woodstock itself.
As time moved forward so did the shift in rock music and a very significant one during the summer of '69. The hard rock sound of Led Zeppelin became mainstream, The Beatles performed for the last time in public and The Who added a rock opera to the mix titled, 'Tommy'.
Initially the Woodstock promoters had laid out a money staging event loaded with concerts for approximately 50,000 people but woah nearly 500,000 came through the gates and a lot of them avoided paying??
Imagine the traffic, yes it was ridiculous, there was very little food, it rained like crazy and it wasn't the facilities were most unsanitary for that size of a crowd, regardless; of all  the organizational failings, Woodstock made musical history.
The Who being The Who became instant superstars, they performed a 24 song set, you had Pete Townsend smashing up guitars and throwing them in the crowd (priceless). Jimi Hendrix rendition of "The Star Spangled Banner"  considered the best in his career despite the controversy and throw in a stellar performance of "Soul Sacrifice" by Carlos Santana and you have classic rock history.
Sounds of the Summer of '69:
Led Zeppelin - LP 'Led Zeppelin'
Jethro Tull - LP - 'Stand Up'
Santana - LP  - 'Santana'
Neil Young - LP - 'Everybody Knows This Is Nowhere'
Blind Faith - LP - 'Blind Faith'

The Who perform, the rock opera "Tommy"