How do you go to mahogany town

In Pokemon Crystal, Go to Ecruteak City. Head right until you reach route 42 and surf across the water. Just keep going right until you reach Mahogany Town.
You can also go through Mt. Mortar from Ecruteak. Go in, straight, right, and head through the passageway. Go right and down through another passageway. Down, right, down the stairs and out of the cave. Head right to Mahogany.