@osma Depth 1400 m (YLE didn't find this worth mentioning). Actually with our bedrock, pumped-hydro installations could be built pretty much anywhere. Using a pre-existing mine saves some excavation work, which is inexpensive anyway using explosives.
https://en.wikipedia.org/wiki/Pyh%C3%A4salmi_Mine
#PyhäsalmiMine #PumpedHydro