Suzy's Cave

Suzy's Cave is a small inland sea arch on Isle Royale's Rock Harbor side, tucked between Rock Harbor and Three Mile Campground. You reach it on foot as part of a roughly 3.8-mile loop, so it's a geology stop on a forest-and-shore walk rather than a quick hop from the dock. The opening itself is modest; the route and the old rock arch are as much the reward as the cave.

From Rock Harbor, follow the Rock Harbor Trail past Rock Harbor Campground to the wooden post and turn inland on the spur to the cave. The loop returns on the gentler Tobin Harbor Trail. The route is unpaved, narrow, and covered in rocks and roots; the Rock Harbor leg is the tougher half. Take that way out and save the smoother Tobin Harbor leg for the return. Allow two to six hours for the round trip. Pets aren't allowed on the hike.

Wave action shaped the opening about 4,000 years ago, when water levels were higher. Isle Royale's sea arches formed where tougher bases of the Portage Lake Volcanics remain after softer tops of old lava flows wore away. That broad, uneven rock bridge over the dark opening is the feature to look for.

The approach passes through spruce, fir and birch, with lake and shoreline views along the way. Slow down under the trees and watch for moose and other wildlife. For a photo, keep the broad rock lip and dark opening in the same frame; crop away the roof and the arch can stop reading as an arch.