The primary attraction is the wilderness of the island. Although it isn't "untouched" – Isle Royale has a history of human habitation and exploitation, and the trails and campgrounds are inherently non-virginal – the remoteness and careful management of the island have combined to make for one of the more authentically "wild" experiences within the National Park system. The trails generally adhere to leave-no-trace principles.
Secondarily, there's the wildlife. Sightings of small fauna such as squirrels and songbirds are inevitable. Fox, moose, and loon encounters can be expected if you look for them and perhaps even if you don't. Signs of the island's wolf presence e.g. footprints and scat are common, and even nighttime howls or a chance glimpse through the trees are just common enough to keep hikers' eyes and ears open for them. Moose commonly use the island's trails as well, and leave plenty of droppings. When populations are high, moose sightings are fairly common. Their numbers have been low recently, however.
Depending on solar activity and magnetic field fluctuations, the aurora borealis "Northern Lights" is frequently visible. On clear nights, the lack of light pollution offers outstanding star-gazing opportunities at lakeshores where the tree cover breaks.
The island's human history is also worth exploring. Surrounding Isle Royale there are several lighthouses you can visit e.g. Rock Harbor lighthouse and Edisen Historic Fishery across the harbor from Daisy Farm campground, Passage Island lighthouse a few miles beyond Blake Point into Lake Superior and shipwrecks e.g. the cruise ship America just below the surface at the mouth of Washington Harbor, and few more several miles farther out. The remains of abandoned copper mines can be found near McCargoe Cove, on the Island Mine Trail, and near Windigo.
