The island would only take perhaps a week or two to cross if it were flat, however the various geographic challenges involved mean it can take months to traverse.
The islands most distinctive features are the twin mountains that make up each side, with a deep valley inbetween.
The smaller side is more populated/explored, and consists of a stony cliff region bordering the ocean, with ruins of an old society, a clay dense region, with many ranches, and then the top of the mountain is covered in a thick bamboo forest. slightly lower down towards the ocean is a small desert region.
The Valley itself is made of fields of wheat and other crops, with towns dotted throughout. the lake/river that splits the valley in two is populated by a variety of sea life, though not enough to sustain the island.
The other peak meanwhile is much less explored, and has only a small number of towns, though most of them are larger than other towns on the island.
It is almost entirely a clay dense region, though there is a desert region against the ocean. This area especially is rich in gold, and copper.
Beneath the second peak is a large cave, full of plant life. This cave is almost entirely unexplored, other than slightly at the ocean level.