Vancouver Island is a large island off the coast of British Columbia, not far from Vancouver city. Most travellers will be arriving there from Vancouver or its environs (although it's also possible to travel to the island from the US).
The island is 270 miles long (stretching roughly along the NW-SE axis) and approximately 70 miles wide, although the spine of the island is mountainous while the coast often indented and thus the actual road distances are much larger.
The principal way of travelling to Vancouver Island is by using the services of BC Ferries. Vancouver has two ferry terminals, one south of the city in the suburb of Tsawwassen (technically in Delta) and another in the north west (technically in Western Vancouver) at Horseshoe Bay.
Vancouver Island has a lot to offer to a visitor: a charming and cultured city of Victoria is the obvious destination, but it's up-island that the best destinations are.
North of Victoria is the second biggest city on the Island, Nanaimo, with an attractive waterfront area and some decent accommodation, and north of it, Parksville and the coastal strip up to Campbell River, which among others includes Qualicum Beach, a picturesque and arty seaside town with more gentle beach.
Parksville itself is unexceptional but makes a very convenient base for exploring Vancouver Island, sitting as it is on a junction of roads going north towards the Comox valley, Campbell River, mountains of Strathcona; south to Nanaimo and Victoria and west via Port Alberni to Pacific Rim National Park with Tofino and Ucluelet.
The best known destination for the lovers of wilderness is the Pacific Rim on the west coast. Originally, most of the Vancouver island was covered in forest, bust as it has been intensively logged for over a hundred of years, there are only relatively small vestiges of this original forest left. Some of it has been preserved as part of the Pacific Rim National Park, which incorporates incredible old-growth temperate rainforest, beaches, rock formations, caves and sea stacks, streams and waterfalls.
The Park is divided into three separate units. The West Coast Trail is a 75 km hiking trail accessible only on foot or (in an emergency by boat, starting at Pachena Bay south of Bamfield). This is a gruelling seven day hike, with limited access points and a lot of rough, wet and muddy terrain. The Broken Group Islands form archipelago of over hundred islands scattered throughout Barkley Sound between Ucluelet and Bamfield and is only accessible by boat, with some local operators offering kayak drop-offs. The most popular, accessible and the smallest of the Pacific Rim National Park units is the Long Beach, located between Ucluelet and Tofino.
Nearer to Parksville the interior has plenty to offer. Within an approximately half hour drive (and some accessible by public transport via the bus to Port Alberni) are three outstanding nature parks, including Englishman River Falls, Quallicum Falls and the best of all, Cathedral Grove.
Further north, Comox valley has some skiing in the winter and beyond that, Campbell River offers excellent fishing, whale watching, and an easy ferry connection to the picturesque and unspoilt island of Quadra.
Beyond Campbell River things get considerably wilder and less populated. Many visitors head for Port Hardy, which is where BC Ferries' vessels depart for trips along the Inside Passage all the way to Prince Rupert via Bella Coola.
Vancouver Island offers incredible wilderness, wonderful landscapes, great surfing, fantastic hiking and friendly, down to earth, often quirky people. The city of Victoria is a sophisticated urban centre which provides a great contrast to the wilderness of the up-island areas. The climate is relatively mild, and the tourist infrastructure exists but doesn't overwhelm. All in all, Vancouver Island is one of the best places in British Columbia and whole Canada to visit and deserves at least a week, and will easily fill several weeks of exploration.