Congratulations (??), you have found a giant tentacle, buried deep in the structure. That tentacle belongs to a even larger being that hides deeper inside. This tentacle alerts to movement in the room its in and will try to grab whoever is the closest and try to strangle them.

The tentacle has magic cancellation properties, so if an item that has magic gets in touch with it, the magic will disappear (it can be fixed on a later date). Any magic that's not an item will just stop working when it hits the tentacle.

To counter the powerful magic cancellation, the tentacle is very weak to physical damage.

There's nothing else in the room. Just this giant tentacle. It may be a good idea to run before anything bad happens.

But what do you want to happen in this situation? The ball is in your court.