Mount St. Double Dare is an obstacle in Double Dare.
In the 2018 revival, it is always the 8th and last obstacle on the course. It consists of a mountain looking like a volcano with green slime "lava" flowing down it. When contestants reach this obstacle, they have to climb up it, grab the flag, then climb back down in order to finish off the obstacle course and win the grand prize.
A running gag in the 2018 series is Liza getting startled by the smoke that comes out of it before she explains how to get through it.