There are a few maps with tombs in them in the tower defence game Gemcraft Labyrinth, they are often heavily armored and take a while to break open, with a swarm of shadow monsters coming out.
I've mostly avoided opening the tombs until I am strong enough to stop these. What is the reward for opening and defeating one of the tombs? What about maps where there are more than one tomb? Do you get battle amulets, skill points if you defeat one but not the other?