The Falls of the Hounds is a massive waterfall that lies along the route of Blaine the Mono, between the cities of Rilea and Dasherville. They are much larger than Niagara Falls. The waterfall gets its name from the rock formation in the middle of it, which resembles two dog heads.
The Old Ones harnessed the energy of these falls. They set up a system where Blaine could recharge his batteries from the falls. Blaine would come to a stop some distance from the waterfall and energy would be delivered to the train in the form of a laser.
It's hinted that the technology could've been made by a civilisation predating the Old Ones.