Chandler goes to the steam room in Season 7, Episode 3, The One with Phoebe's Cookies. The main storyline of the episode involves Monica trying to recreate the recipe for some special cookies. Ross's Dad, Jack, invites Chandler to play racket ball with him and Ross since Chandler is now engaged to Monica. After their game, they all go to the steam room, but Chandler cannot see well and sits on top of Jack, while both are unclothed. Chandler is embarrassed and goes to play ball with Jack another day, only to remove his clothes thinking they are in a steam room, when they are really in a pool room.
Chat with our AI personalities
Season 9, Episode 19, The One With Rachel's Dream
Chandler asks about the fish in The One with Phoebe's Ex-Partner (season 3 episode 14)
The episode when they (Tohru, Kyo, Yuki and Momiji) go to the hot springs is episode #12 called White Day.
Chandler proposed to Monica in Episode 25, Season 6: "The One with the Proposal, Part 2"
Maybe the one where Monica and Chandler go see Chandler's father (as played as a drag queen by Kathleen Turner). I believe she does a cabaret number.