Biking -- The Lower Keys are a great place to get off busy U.S. 1 to explore the beautiful back roads. On Big Pine Key, cruise along Key Deer Boulevard (at MM 30). Those with fat tires can ride into the National Key Deer Refuge. Many lodgings offer bike rentals.
Bird-Watching -- A stopping point for migratory birds on the Eastern Flyway, the Lower Keys are populated with many West Indian bird species, especially in spring and fall. The small, vegetated islands of the Keys are the only nesting sites in the U.S. for the white-crowned pigeon. They're also some of the few breeding places for the reddish egret, roseate spoonbill, mangrove cuckoo, and black-whiskered vireo. Look for them on Bahia Honda Key and the many uninhabited islands nearby.
Boating -- Dozens of shops rent powerboats for fishing and reef exploring. Most also rent tackle, sell bait, and have charter captains available. For instance, Florida Keys Boat Rental (tel. 305/664-2003; www.keysboat.com) offers an impressive selection of boats from $125 to $450 for a half-day and $105 to $650 for a full day. They also offer kayaks and paddle boats for eco-tours.
Canoeing & Kayaking -- The Overseas Highway (U.S. 1) touches on only a few dozen of the many hundreds of islands that make up the Keys. To really see the Lower Keys, rent a kayak or canoe -- perfect for these shallow waters. Reflections Kayak Nature Tours, operating out of the Old Wooden Bridge Fishing Camp, 1791 Bogie Dr., MM 30, Big Pine Key (tel. 305/872-4668; www.floridakeyskayaktours.com), offers fully outfitted backcountry wildlife tours, either on your own or with an expert. The expert, U.S.C.G.-licensed Captain Bill Keogh, literally wrote the book on the subject. The Florida Keys Paddling Guide (Countryman Press), written by Bill in 2004, covers all the unique ecosystems and inhabitants as well as launches and favorite routes from Key Biscayne to the Dry Tortugas National Park. The 3-hour kayak tours cost $50 per person. An extended 4-hour backcountry tour for two to six people costs $125 per person and uses a mother ship to ferry kayaks and paddlers to the remote reaches of the refuge. Reservations required.
Fishing -- A day spent fishing, either in the shallow backcountry or in the deep sea, is a great way to ensure a fresh-fish dinner, or you can release your catch and just appreciate the challenge. Whichever you choose, Strike Zone Charters, U.S. 1 at MM 29.5, Big Pine Key (tel. 305/872-9863; www.strikezonecharter.com), is the charter service to call. Prices for fishing boats start at $650 for a half-day and $850 for a full day with the possibility of a $50 fuel surcharge added to the cost. If you have enough anglers to share the price (they take up to six people), it isn't too steep. The outfitter may also be able to match you with other interested visitors. Strike Zone also offers daily trips to Looe Key National Marine Sanctuary on a glass-bottom boat. The 2-hour trip costs $25 for viewing, $35 for snorkeling, and $45 for scuba diving, all with a $3 per person fuel charge. Strike Zone's 5-hour Eco Island excursion offers a vivid history of the Keys from the glass-bottom boat. The tour stops for snorkeling and light tackle fishing and eventually docks at an island for their famous island fish cookout. Cost is $55 per person plus an additional $3 surcharge for fuel, including mask, snorkel, fins, vests, rods, reel, bait, fishing licenses, food, and all soft drinks.
Hiking -- You can hike throughout the flat, marshy Keys on both marked trails and meandering coastlines. The best places to trek through nature are Bahia Honda State Park, at MM 29.5, and National Key Deer Refuge, at MM 30. Bahia Honda Park has a free brochure describing an excellent self-guided tour along the Silver Palm Nature Trail. You'll traverse hammocks, mangroves, and sand dunes, and cross a lagoon. The walk (less than a mile) explores a great cross section of the natural habitat in the Lower Keys and can be done in less than half an hour.
Snorkeling & Scuba Diving -- Snorkelers and divers should not miss the Keys' most dramatic reefs at the Looe Key National Marine Sanctuary. Here you'll see more than 150 varieties of hard and soft coral -- some centuries old -- as well as every type of tropical fish, including gold and blue parrotfish, moray eels, barracudas, French angels, and tarpon. Looe Key Dive Center, U.S. 1 at MM 27.5, Ramrod Key (tel. 305/872-2215; www.diveflakeys.com), offers a mind-blowing 5-hour tour aboard a 45-foot catamaran with two shallow 1-hour dives for snorkelers and scuba divers. Snorkelers pay $44, children 6 and under pay $34; divers pay $84 for three dives, $69 for two. Equipment is available for rental for $10. On Wednesday and Saturday, you can do a fascinating dive to the Adolphus Busch, Sr., a shipwreck off Looe Key in 100 feet of water, for $50 with $30 per additional diver.