The 113-mile (181-kilometer) drive on Highway 1 from mainland Florida to Key West induces sensory overload. Besides the natural beauty along the route—tidal flats, teal waters dotted by distant islands—the so-called Overseas Highway awes you in its own right as an engineering marvel. Its concrete stretches across impossible expanses of water, the Atlantic spreading out to the left, the Gulf to the right.

Overview
Highway 1 is festooned with classic Americana, from kitschy gift shops purveying seashell necklaces to burger stands offering shakes and fries. But that's just the half of it. Beneath the ocean surface lies a separate world of Technicolor fish and coral reefs. Below are the five best dive sites you'll encounter as you proceed from Key Largo, near the top of the island chain, down to Key West, at the end. At each spot, you'll park at a dive shop and motor out to the reef on a boat. The entire dive experience takes two to four hours, leaving ample time to watch the sunset and enjoy a seafood dinner. Meanwhile, non-divers will find plenty else to do, from snorkeling to exploring state parks to visiting museums. Major attractions are sited by mile marker, from MM 107 in Key Largo to MM 0 in Key West.

Begin in Key Largo
Key Largo calls itself the dive capital of the world. It's home to the 70-square-mile (181-square-kilometer) John Pennekamp Coral Reef State Park (MM 102.5; 451-6300; www.pennekamppark.com). The park has a visitors center and beach, a good place to hone your snorkeling skills before boarding a dive boat. The best undersea attraction of the Florida Keys National Marine Sanctuary (floridakeys.noaa.gov) is the wreck of the Spiegel Grove (www.fla-keys.com/spiegelgrove), a 510-foot (155-meter) retired Navy ship sunk as an artificial reef in 2002 and now resting 130 feet (39 meters) underwater near Dixie Shoal. Fish you might spot include trumpetfish and angelfish lurking along the hull, which is covered with sponges and soft coral. You can also stop at Molasses Reef, suitable for snorkelers. Local dive operators include Ocean Divers (522 Caribbean Dr.; 451-1113; oceandivers.com) and Amy Slate's Amoray Dive Resort (MM 104.5; 451-3595; www.amoray.com), which offers morning coffee with its rooms and apartments.

Pennekamp
In the area: Locals stop by the Marlin (MM 102.7; 451-2454), a Cuban restaurant, for a café con leche and pastelitos (crispy, filled pastries; try the guava) before turning in to Pennekamp. After your dive, try Hobo's Cafe (MM 101.7; 451-5888; hoboscafe.net), an authentic Keys eatery serving burgers and fresh fish.