kiosk, pavilion
榭 centers on a small, open structure for rest or enjoyment: a kiosk or pavilion, typically built on a raised platform.
榭 combines 木 (tree, wood) with 射, which likely contributes the sound. The character originally referred to a wooden pavilion or raised platform.
A wooden 木 structure that looks like it was shot 射 into place: a pavilion or kiosk standing on a platform.
For シャ, imagine a pavilion casting a sharp shadow: sharp -> シャ, and the wooden kiosk stands in the shade.