For me:
The few buzzer beater moments of solving a puzzle where everything comes together just as time runs out. There have been a few but notably I remember an early room in one of the Rothfus dungeons where there was a large chest with stencils of adventurers and I think it turns out they were representations of clock faces.
Also a later room in the same dungeon where we had to match alchemical reagents with their containers, which was destructive and involved multiple senses - things that are cold to the touch, magnetic, bounced/deformed differently.
Other stand outs:
- Seeing Smoak for the first time and the DM throwing our consumables into his hoard.
- Early dungeon with detect secret doors / secret writing / comprehend languages giving UV light source and a ghost / wight rising in a graveyard
- the cup and ring puzzle where the answer was the cups are really bells and organized by sound
- first run with some friendly tokenaholics who had healing buffs for everyone
- seeing the War Maul of the Ancients in action on a run with Smakdown
- see the Hammer of Foss Altus special token at the first TDC
- completing / surviving a two man nightmare dungeon after surrendering all gear but one token to a troll who you could bribe that way to avoid a fight in TDC
- all the forum greats of yesteryear who I got to talk with any don’t post much anymore - too many to list but Henwy, Chad, Master Ed, Arcanist Kolexia, Adela, Hawk Fingle, Eversuede, George, Brad Mortensen, valetutto, Steve, harlax, Incognito, Dennis Burdick, Widseth, Druegar all come to mind.