The Pool of Rain

The Pool of Rain is a rained pool found in Wario Land 3 of the Wario Land series. It serves as the third of six levels found at the west side of the Music Box World. Wario, in search of the five Music Boxes, cannot reach this place, because there is no rained water in the empty pool. However, after finding the Jar of Rain in Out of the Woods, a rain cloud pops out which causes itself to rain in the empty pool, opening the path to The Pool of Rain in the process.

Grey Chest: The Cog Wheel A
The treasure of the Grey Treasure Chest is across several small brown platforms over the pool. If you do a ground pound on one platform, it will sink, but at least one other platform will rise. If you force a platform high enough, you can reach higher platforms, allowing you to get the grey Key and Treasure Chest. If you mess up by falling off into the water below, you will have to try the part you messed up again. The second part contains an area with a long high platform that you need to ground pound small platforms for others to rise so you can get the grey Key on the long platform.

When the Cog Wheel A is placed into the elevator, though you have to get the Cog Wheel B in A Town in Chaos too, the elevator will work with both Cog Wheels that makes a path to The Grasslands.