“ My treasure? [...] I have it here. Would you like to see it? Uhhh... Uh, oh... Aha, ha ha. I lost it. The stuff inside, too. Gone! Ah, well. It's probably lying around here somewhere. If you find it, you can have it. ”
The Boss' Treasure (カシラの大事なもの, Kashira no Daijinamono, lit. Boss' Important Thing) is an event in Tomba!.
Find the boss' lost treasure.
Talk to the man in red found inside the room with the small keyhole to activate the event. He will mention his treasure and then realize that it's gone, offering Tomba to keep it if he finds it. He will head outside and the event activates.