• What to do: Some 15,000 years ago, as the last glaciers of the Wisconsin Ice Age retreated back to Canada, a huge hunk of ice was left in a shallow valley. It's massive weight sunk into the soft, wet ground and its meltwater filled the depression, forming what became the 64-acre Lake Pleasant near what is now Arbuckle in Erie County. Unlike the acidic "kettles," or glacial lakes, of the Pocono region, Lake Pleasant's alkaline chemical balance has made it suitable for more than 80 species of plants, including 24 of special concern, and three rare fishes. Draining into French Creek, Lake Pleasant is widely considered the most interesting and beautiful of Pennsylvania's glacial kettles. It's managed by the Western Pennsylvania Conservancy; fishing from shore and motorless boats is regulated by Pennsylvania Fish and Boat Commission.

• Contact: Western Pennsylvania Conservancy 412-288-2777

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