island
嶌 centers on an island, specifically a landmass surrounded by water, often with mountainous terrain.
嶌 is a variant form of 島, combining 山 (mountain) and 鳥 (bird). The original 島 likely depicted a bird resting on a mountain in the sea, symbolizing an island. 嶌 is a less common graphical variant.
A mountain 山 rises from the sea, and a bird 鳥 perches on it: this isolated spot is an island.
For トウ, imagine a bird flying to the island: 'to' the island -> トウ.