“Underground” is mentioned in the text above. I know that some people are considering to store heavy blocks connected to ropes in the shafts (?) of old coal mines that go down hundreds of meter. Use a single, very heavy block and you’re good to go. Though I don’t think that it holds a significant amount of energy (too lazy to calculate and no feeling for the possible dimensions of such a block). Also, digging new shafts should be prohibitively expensive for energy storage.