Danger room
From SpiralKnights
Danger rooms are optional areas sometimes found within Clockwork Tunnels. They are a pay area that costs 3 energy. Inside the gate, the danger room is a single room with a party button where the gates will not open until all the monsters are defeated, similar to Battle Arenas. Past the danger room is a treasure room if you successfully defeat the enemies.
There are three known danger room layouts: