My players are so high level guys. 5 players all level 14 soon to be 15

A wizard A rouge A warlock A fighter A samurai

They are dastardly good at the game, and I find it hard to challenge them in combat now. We just met the Githanki, made some red dragon friends, and now we want to attempt to wage war on the mind flyers on the floor below.

I've never ran a campaign at this level, so I'm trying to bring back the challenge.

They stomp anything I put in front if them unless I make up the HP😂

We killed a terasque floors ago for fun. That was our last challenge.

What are some non “hit point” or “damage done” related ways to challenge characters? Make it challenging?

I've done the “remove their items and abilities and use your wits” thing once or twice and its worked, but I'm running out of options.

They seem like they will just walk down halistar and murder his ass 😂

Help please?