The Fjords of Chile are beautiful and accessible by ferry and this is the only way to experience these wonderful sights. If you are interested in navigating the Fjords of Chile, then it is done by taking a multi-day ferry from the southern port city of Puerto Natales to Puerto Montt or the reverse.
Click this map link to see the approximate route for this excursion.
Booking this excursion can be done online at the Navimag web site. You can select an English language version and the web site will have more detailed information. You board the vessel in the afternoon around 16:00 hours, find your berth, have an evening meal, sleep and while you are sleeping the ferry departs at about 6:30am the next morning. The first night is considered the evening in which you board and wait for the ferry to depart.
I have personally done this route from Puerto Natales to Puerto Montt. It was in the month of February which should be their high season so prices will reflect this.
Bring some sort of rain wear as regardless of time of year, there will be some sort of precipitation during the daylight travel hours.
Travel Safe, Travel Happy