Expeditions' ferries cross the channel five times daily, departing from Lahaina on Maui and Manele Bay Harbor on Lanai. The crossing takes 45 minutes and costs $25 each way. Be warned: passage can be rough, especially during winter. On the flip side, you'll see plenty of whales along the way.
Expeditions (808/661-3756 or 800/695-2624. www.go-lanai.com).
If you are staying at the Four Seasons Resort Lanai at Manele Bay or the Lodge at Koele, transportation from the harbor is almost effortless; the resort staff accompanies you on the boat, and shuttles stand ready to deliver you and your belongings to either resort. If you aren't staying with the Four Seasons, it's pretty much the same drill -- the bus drivers will herd you onto the appropriate bus and take you into town for $10 round-trip. Advance reservations aren't necessary (or even possible), but be prepared for a little confusion on the dock.
Lanai City Service (Lanai Ave. at 11th St. 808/565-7227 or 800/533-7808).