my tiretrack eel has a cave... it's his cave.. unless my 2 Sens are bored. I swear they kick him out.. and play hide and seek .. they're crazy... they only do it at night though.. and are flitting around the tank all day.. I have to say they are by far one of the weirdest fish I've ever had and also hilarious to just sit infront of the tank and watch. They are like takeing a dog and putting it into a fishtank..