I have climbed Mt Katahdin twice. Make sure you dress for any condition. Last time we climbed, it was warm at the bottom and windy and cold at the top, in the middle of August. For a roundtrip climb, hike in through Chimney Pond (there are several ways to get there) and either go up Cathedral trail or across Knife’s Edge or vice versa. It’s a beautiful climb. On a clear day you can see all the way to the Atlantic and Mt Washington.