Expect a great deal of interesting Key West history, beautiful gardens, and the ultimate view for you at the top. Yes, lighthouses had a very strategic purpose back in the day. This one built just after the first one was blown away by hurricane in 1846. The Key West reefs cause all kinds of issues for our captains of large sailboats, they need depth. Its objective was simple, be an easy to see navigational guide for captains to make directional coordinates from.
It was very cool to see. Tour Mr Keeper's Quarters and learn about the flavorful people that were among those that tried to prevent the shipwrecks. Children will love heading all the way up to the top. No parachutes allowed!
Pick a very clear day to enjoy the best views from up top. There is plenty of goodies to see in Old Town. My top picks would include the Southernmost Point Buoy, Truman Annex, Aquarium (a family place), Mallory Square, Martello Gallery, and Audubon House. For food, go with Grilled Mahi-Mahi Sandwich (served with lettuce, tomato, onion, tartar sauce, key lime wedge, and french fries) at the Roof Top Cafe, by Mallory Square.