The Overseas Highway (US-1) officially starts in Florida City, near the Everglades some 50 miles south of Miami, but doesn’t really come alive until it leaves the mainland and lands at Key Largo, the first and largest of the dozens of “keys” (from the Spanish word cayos, meaning small islands) that the highway links together. The Overseas Highway reaches Key Largo at the popular John Pennekamp Coral Reef State Park (MM 102.5, 305/451-6300, daily, $8 per car). The first place where you can really get a feel for life on the keys, the park is the starting point for a variety of guided tours (scuba diving, snorkeling, or in glass-bottomed boats) that offer up-close looks at the only tropical coral reef in the continental United States and all but guarantee that you’ll see enough sealife to fill a photo album or two. Along with the adjacent Florida Keys National Marine Sanctuary, the park gives access to more than 175 square miles of diving spots, including reefs, shipwrecks, and a nine-foot-high bronze statue called Christ of the Deep. The visitors center has a replica reef in a 30,000-gallon aquarium full of colorful fish, allowing a quick look at the fascinating underwater world without getting your feet wet; the park also has a pleasant campground.

Film fans will know that Key Largo was the title and setting of a great 1948 film noir movie starring Bogie, Bacall, and Edward G. Robinson; these days, it’s also home to the co-star of another classic, the boat from the African Queen, which is moored next to the Holiday Inn at mile marker 100 and provides daily canal cruises. Most of Key Largo today, however, is a rather tawdry four-mile stretch of seashell stands, dive shops, boat shops, and margarita bars; there are many good restaurants, including Mrs. Mac’s Kitchen (MM 99.4, 305/451-3722, Mon.-Sat.), a small and friendly place with inexpensive food and more beers to drink than seats to sit on.

Key Largo also has many good places to stay, from the funky Sunset Cove Beach Resort (MM 99.3, 305/451-0705, $135 and up) to the boutique Azul del Mar (between MM 103 and MM 104, 305/451-0337, $179 and up), a relaxing small resort. Also here is the truly unique Jules’ Undersea Lodge (305/451-2353, packages from $150 per person for a three-hour visit only), a two-room motel that is 21 feet beneath the sea—a quick scuba dive down from 51 Shoreland Drive, off mile marker 103.2.