You will use the parks here on the island more than you would have anticipated. The area is great for walking and we toured the island often. Enjoy the city park which is huge, Sunset Park for after dark skinny dipping, sharkys for drinks, and the awesome Cabana Club swimming pool area.
I have been doing research for our October Keys vacation. So far, it looks like Key Colony Beach is a Great Place to Stay and it is near Marathon. The little park on the end is part of its charm. It has a lot going for it - all condos/homes are on canals with Boat Dockage, and the boat dockage is nice, not like that flim-flam dockage at Pines and Palms.
Yeah, Boater Friendly Condos with Boat Dockage, all dog friendly! They rent condo here on a weekly basis, but you can choose your days (no Saturday to Saturday rule). The big Fantasy Fest parade is the last Saturday in October. I can ask to have off the week of Oct 25th so we can go.
Waterfront spots to enjoy in Greater Marathon are everywhere. The island is blessed to have some really neat places that mainly only locals know about. Coco Plum Beach Park is a winner and dog friendly for those with fido. Probably the sweetest waterfront location to check out is Sombrero Beach.