The West Highland Line from Glasgow Queen Street via Fort William is the obvious way in. The full journey takes about five hours and ranks consistently among the great rail trips of Europe — over Rannoch Moor, around the head of Loch Eil, across the Glenfinnan Viaduct and down to the sea at Arisaig. A scheduled ScotRail service runs the line all year; the steam-hauled Jacobite operates the Fort William–Mallaig section in summer.
By road, the A830 ("Road to the Isles") from Fort William takes about an hour and a half and is well surfaced throughout. Coming from the south, an alternative is to ferry from Lochaline to Fishnish on Mull, cross the island, and rejoin the mainland at Kilchoan or Ardgour — much slower but spectacular and almost traffic-free.
CalMac ferries from Mallaig serve Armadale on Skye (about 30 minutes), the Small Isles of Canna, Rum, Eigg and Muck (anywhere from one to three hours), and Inverie on Knoydart (45 minutes, pedestrians only). The Skye crossing books up in summer if you have a car; reserve in advance.