A good place to start a riverfront stroll, Coolidge Park has a play fountain, a carousel ($1 per ride), well-used playing fields, and a 50ft climbing wall attached to one of the columns supporting the Walnut Street Bridge, one of the world's largest pedestrian bridges.
Abutting the park, the city has installed gabions to restore the wetlands and attract more birdlife. Check them out by strolling to the edge of the cool floating decks that jut over the marsh.