Almost each gym has a  gimmick. A puzzle of sorts you need to complete to get to the leader. Out of all the gym gimmicks ever in the series which are your favorites?

 

For me, my favorites are:

Blaine's (optional) quiz game in Cinnibar

The ice sliding puzzle in Mahagonny (both the regular and heartgold/soul silver versions)

Norman's different stat rooms in Petalburg 

Wallace/Juan's ice puzzle in Sootopolis

Snow puzzle in Snowpoint (in all versions)

Nimbasa's roller coaster puzzle in BW1

 

Skyla's cannons in B/W. I mean, one makes you crash into a fricking wall. She's practically trying to murder those who aren't strong enough to challenge her.

Snow puzzle in Snowpoint (in all versions)

Remember the Snowball one in D/P/P

I had to follow the walkthrough from youtube ...  

Nimbasa's roller coaster

Skyla's cannons

Norman's different stat rooms

I like the dragon puzzle thing in the eighth gym in Black/White.

...I thought you meant a proper gym

 

Like introductory free sessions

Cheap monthly memberships

Half price instructor sessions

Free classes....

etc

I love Skyla's gym in both BW games. I really doubt they would pass any OSHA inspection.Other favorites are the flashlight puzzle in Fantina's gym, the slippy slidey ice puzzle in Pryce's gym, the gate puzzle in Winona's gym, and Celadon city's just for the flavor text with the old man outside of the gym.