Every half-hour, visitiors can take a 25-minute tour of Prospect Park Lake, a 60-acre, man-made creation. The tour starts at the Prospect Park Audubon Center and continues through the Lullwater, opening into the lake itself. Not a bad way to spend an lazy Brooklyn afternoon. Prices are $5 adults; $3 kids age 3-12. In the summer and spring, through the end of October.