There are a wide range of one-way hikes made possible by Island Explorer buses. Here are a few sample hiking expeditions:

Hike from Sieur de Monts (Bus 3 or 4) to the Jordan Pond House (Bus 5).

Head from the Brown Mountain Gate House (Bus 6) over Sargent Mountain to Jordan Pond or Bubble Rock (Bus 5).

Hike the full length of Cadillac Mountain from the North Ridge (Bus 3) to Blackwoods (Bus 4).
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Head from Sieur de Monts (Bus 3 or 4) across Champlain to Sand Beach (Bus 3).

These are steep and strenuous trails. Take a map, trail guide, and plenty of water. Do not underestimate the time required. Start early so you don't miss the last return bus at the end of your hike.