Pumped storage is an emission-free and relatively cheap method of generating power at peak times. The idea is to pump water up to a reservoir at the top of a mountain at night (off-peak) when electricity is cheap. Then at peak times, when everybody needs electricity, you can use the pressure head of the elevated water to drive a turbine and generate power.
The problem is that good sites are rare, difficult to find, develop, permit, and operate. One solution that may work for some areas could be to take the whole setup and move it down into the Earth. Dig a tunnel or use existing cave systems that are deep in the ground. You would have the powerplant chamber and turbine deep underground, but the reservoir and all the other facilities could be easily accessible at ground level.
Image adapted from: http://www.tva.gov/power/images/pumpstor.jpg
IDEATION: November 3, 2008.