A 1987 Geological Society of America report [pdf] describes the ledges, their formation, their fossils, and their geology. "The Ledges of the Grand River are the best exposure of Pennsylvanian age rocks in the state of Michigan. Besides their scenic beauty, the Ledges and additional outcrops of the surrounding vicinity provide a unique setting in which to explore and investigate an ancient near-shore marine beach environment."
Fitzgerald County Park provides the easiest access to the ledges, with plenty of parking ($5 vehicle access fee) and a stairway down to the Ledges Trail. The park has a few other short nature trails in a downstream forested area. Other amenities include a playground, disc golf course, restrooms, picnic areas, ball diamonds, a theater, and a small nature center. The sandstone in the park is covered with velvety lichen, mosses, and ferns.
Google identifies the footpath running from Grand Ledge to Fitzgerald County Park as the "Riverwalk" but local signs label it the "Ledges Trail". It's not a boardwalk but a dirt path halfway down the riverbank. It's under a mile from Island Park at the edge of the business district to the railroad bridge that marks the boundary of the county park.