The standard approach is overland from Puerto Montt and then the short Chacao ferry crossing to the northern tip of Isla Grande. Regular buses from Puerto Montt's bus terminal run directly to Castro and Ancud; the journey including the ferry takes about 2 hours to Ancud and 3 hours to Castro. The ferry crossing at Chacao takes about 30 minutes and runs continuously throughout the day.
There are also direct flights from Santiago to Castro's small Gamboa Airport (IATA: WCA), operated by Latam. Flight time is about two hours, significantly faster than the overland journey from Santiago, which takes 12 hours by bus.
In the far north of the archipelago, the Hornopirén-Caleta Gonzalo ferry offers an alternative route south toward Patagonia, combining the archipelago with the Carretera Austral without retracing your steps — a popular choice for travellers heading south.