1. He went on lots of exciting rides.
2. He went on doing lots of exciting rides.
3. He went to lots of exciting rides.
(Are both OK? What is the part of speech of 'on'? Is 'on' an adverb? Can't we use as in #3?)
Only #1 is okay.
"On" is a preposition here: "on ... rides" is the prepositional phrase.