I'm snorkelling with mermaids under a sparkling blue sky. Their soft chirruping song washes over me, luring passing boaters into warm waters fringed by swaying palms. It may sound like just another cheesy Disney "experience", but this is Florida's other magical kingdom – a wonderland of real-life rivers, beaches and trails a world away from Orlando's theme parks.
For a start, these mermaids are far from little. Weighing half a ton each and sporting scarred, wrinkled hides, they were first recorded in 1493 by Christopher Columbus, who noted with a crestfallen air "they were not so beautiful as they are described". Indeed not. The West Indian manatee is undeniably one of nature's ugliest creations: a wallowing aquatic mammal that combines the liquid grace of a cow with the cuteness of a warthog.
Yet the experience of swimming among them is breathtaking. Unlike nervy dolphins, placid manatees are comfortable around humans, gliding calmly through underwater foliage with calves in tow. Every winter, hundreds congregate at natural hot springs such as this one at Crystal River on Florida's Gulf Coast, sitting out the cooler months until they can venture out again in search of tasty aquatic weeds.
Captain Joe Detrick of Fun 2 Dive manatee tours runs a strict "no touching" policy. Manatees that become habituated to humans stand a greater risk of running into boats and propellers – the leading cause of death for these endangered creatures. We arrive at the spring just as the local volunteer rescue team is reintroducing an injured female manatee. It's all hands on deck as we hold her down, attach a GPS marker to her muscular tail and carry her – five abreast – down to the water. With a whoop from the crowd and a mighty splash, she surges back into the herd.
My next stop is Wekiwa Springs State Park, near the town of Apopka. Why settle for an artificial river ride in a theme park when for a few dollars you can rent a kayak here and explore the unspoilt Rock Springs Run in virtual solitude? Lush vegetation overhangs the clear waters, giving glimpses of alligators basking in the sun, and the pine forest beyond.
The sub-tropical park also has plenty of hiking trails and several camping grounds with basic facilities (don't forget your mosquito spray). Even this close to the freeways and strip malls of Orlando, wildlife abounds. Deer leap over viciously sharp saw palmettos, while sleek, iridescent wild turkey dart through the undergrowth. Among the leaves and fallen branches, a nine-banded armadillo snuffles for insects. These curious creatures are fearless beneath their armoured scales, rooting busily through the dirt for caterpillars, beetles and termites.
If you're itching for something a little faster-paced, explore Orlando's growing network of bike trails. There is a grand plan to link dozens of trails into a huge loop that will surround this sprawling city, giving an -environmentally friendly alternative to Orlando's choking freeways. While that vision is a long way from being realised, the length of cycle-ways on offer is creeping up every year. A great place to start is the West Orange Trail – one of the longest trails in the Orlando area, running 22 miles along an old railway line.
I pick it up at mile zero, where West Orange Trail Bikes and Blades rents cycles – including the smartest road bike I've ridden. I climb gingerly on to a high-tech Jamis 10-speed and head north-west, along the edge of Lake Apopka. The paved trail is empty enough to coax out my inner Bradley Wiggins (fourth in last year's Tour de France), encouraging me to rattle over a wooden railroad bridge, flash through a nature preserve and pass the historic railway museum without so much as dropping a gear.
The sleepy suburb of Winter Park, where I take a rest stop, has a wholesome downtown which could be the template for Disney's Main Street USA, except here the galleries and cafés are more than façades for fast-food restaurants. An Art Deco cinema stages plays where its silver screen once stood. In the brick-built Edgewater Hotel nearby, retro rules. Its polished wood lobby has a gleaming Otis lift, while a vintage diner serves ice-cream floats and elaborate sundaes.
Winter Park has just legalised the use of electric golf carts on the town's streets to cut emissions and calm traffic. Frankly, it's hard to imagine the sedate drivers here becoming any calmer without slipping into a coma. Even weighed down by two scoops of vanilla, hot fudge and a glacé cherry, I am riding the fastest vehicle in town. I speed under shady live oaks, past high-school football practice and soon find myself in central Florida: aggressive residential developments with fluorescent lawns and over-watered golf courses. The miles slip by, and by the time the trail nudges up next to a highway at mile 14, I'm ready to dodge the golf carts and turn for home.
On my last day in Florida, I wonder whether I've been too dismissive of its theme parks. However, the queues and crowds of Universal, SeaWorld and Walt Disney World still don't appeal, so I drive north to the site of one of the state's first purpose-built resorts. De Leon Springs was named after Juan Ponce de Leon, a Conquistador who may have come to Florida in search of the mythical fountain of youth but ended up settling for gold, slaves and land. The park's centrepiece is a spring boil that pumps out 20 million gallons of warm, sulphurous water daily into a swimming area.
In its heyday in the Fifties, De Leon Springs was a bustling holiday destination with a Spanish-themed hotel, river cruises, a "monkey island", fibre-glass dinosaurs and Queenie, a water-skiing elephant. Now a state park with access to 18,000 acres of lakes, creeks and marshes, it has been largely reclaimed by nature. The remains of the hotel have been converted into changing rooms, paved nature trails have crumbled back into eerie cypress bogs, and monkey island is a few scraps of metal poking from luxuriant bushes by the side of a swamp.
After a hike along the park's five-mile Persimmon Trail, I plunge into the steaming waters of the fountain of youth – the only bather apart from an elderly lady dipping her toes. As I float above the surging boil, heated by water from the spring's subterranean depths, I can't help imagining the Magic Kingdom similarly derelict, its rides gripped by mangroves, car parks carpeted with palms, armadillos grubbing bugs from gift shop walls and manatees soaking in abandoned swimming pools.
It's a wonderful vision that could only be improved upon by the addition of a water-skiing elephant.
*British Airways (0844 493 0787; ba.com) and Virgin Atlantic (0844 209 7777; virgin-atlantic.com) fly non-stop daily from Gatwick to Orlando. There are also charter flights from a range of UK airports to the charter airport, Orlando Sanford International Airport. BA also flies to Tampa.
*The Rosen Shingle Creek (001 407 996 9939; rosenshingle creek.com ) has a golf course, swimming pools and luxurious double rooms from $111, excluding breakfast.
*The Edgewater Hotel in Winter Garden (001 407 654 6921; historicedgewater.com) has bed and breakfast from $74 (£49).
*Camping at Wekiwa Springs State Park ( floridastateparks.org/wekiwasprings ) costs $5 (£3.50) per person per night.
*West Orange Trail Bikes and Blades rents bikes (001 407 877 0600; orlando bikerental.com) for $6 (£4) per hour, and $30 (£20) a day.
*Fun 2 Dive scuba and manatee tours (001 888 588 3483; www.fun2dive.com ) has tours for $90 (£60) per person.