The Indian Key Historic Site is one of those places you simply have to go, to truly appreciate. Located just off Lower Matecumbe Key, the 11-acre key was originally home to a small settlement of shipwreck salvagers back in the early 1800's, who made their living off of salvaging cargo from the ships which would run aground the shallow waters.
The best place to park if you have your own kayak or canoe, is in between mile maker's 78 and 79 on a small island just north of Robbie's (Yes the Robbie's, where you can feed the tarpon), you can also rent kayaks and boats at Robbie's.
The paddle over is quite quick and mostly over very shallow water. As you paddle out, aim for the right-hand side of the island (Southern side) which has a doc protruding into the water. There is a small very rocky "beach" where you mostly likely will find several other kayaks or paddle boards already pulled up.
If you bring a boat over, you will need to moor out from the island at the southernmost point. There is a dock but it sits too high to bring the boat up to.
Once on the island, its time to explore. Not much remains of the original town except for some roads, housing foundations and what looked like it could be a cistern. Its still really fun and cool to explore. There are even some plaques with cool facts about the people who used to live on the key.
Indian key is scorching hot, so make sure, if you do head out there, to bring lots of sunscreen, cold water and a snack. Total round trip time is most likely an hour if you head there and then immediately back, so give yourself at least two to three full hours to lend time to exploring and swimming.