Such is the beauty of Mount Desert Island's National Park that visitors, like the local beavers, appear again and again
"And of course at this time of the evening you are likely to see quite a few beavers, particularly if you have a look in the water close to their nests," the ranger told me when I reached Acadia National Park. "Beavers are nocturnal, so sunset is just the right time to arrive." I hadn't the heart to tell him I would be unlikely to recognise a beaver, let alone its nest.

But since there is no shortage of information or advice about the wildlife in the Park - flora as well as fauna - it is difficult to remain ignorant for too long.

Acadia's 40,000 acres cover about a third of Mount Desert Island - Desert is usually pronounced as if it were part of a meal, rather than a dry landscape, presumably a legacy of the pronunciation used by the Frenchman who first named it. The island itself is shaped, appropriately, like the claw of a Maine lobster, and is joined by a bridge to the mainland near Trenton, about two-thirds of the way up the Maine coast on the way to the Canadian border.

The park straddles most of the island, taking in the Somes Sound fjord, but the focal point is Cadillac Mountain, to the eastern side of the island, which is contained within Acadia's best-known attraction, the Loop Road. Although by far the best way to see the park is to walk some of its many trails, a drive around the Loop Road is a good introduction to its huge variety of terrain and wildlife.

There are several entrances, and traffic moves in a clockwise direction only, except in one small section. Start by the Visitor Centre at Hulls Cove in the north and follow the road south, stopping off from time to time as the view changes, for a panorama over the small town of Bar Harbor, or the islands of Frenchman Bay and the Atlantic beyond. At Little Hunters Beach the road cuts inland, and heads north along the side of Jordan Pond, a popular spot for sailing, and from there back to the starting point.

At intervals all along the Loop, walking trails, of varying length and difficulty, are signposted. Some offer nothing more strenuous than a gentle stroll, but there are several that require considerable energy: try the Beehive if you really want a climb. I prefer some of the trails that go up Cadillac Mountain, winding through the trees until they reach the bare rocks above. Marks are painted on the rocks at junctions where there could be doubt about which route to follow, so once you have found the starting point there is no real need for a map. Cadillac has the distinction of being the first place on the North American continent to experience the sunrise each day, and many visitors like to make the climb to see it. I have to confess I have never been one of them.

At the base of Cadillac, on much flatter terrain, are the Wild Gardens of Acadia. Covering a relatively small area, the gardens nevertheless have examples of many of the native plants growing on Mount Desert Island, grouped together in sections: pond, bog, mountain, seaside and so on. Some of the plants are familiar, but most are labelled so that it is easy to identify any that are not often seen in this country.

The state of Maine is known particularly for its coastline, longer, at three and a half thousand miles, than the whole of the rest of the east coast of the US. But the interior is equally attractive, with its lakes, rivers and mountains, and a section of the Appalachian trail. Part of the charm of Acadia is that it has many of these attractions, while still being within sight of the ocean.

If there is a drawback to the Park, it is the ban on swimming in many of the lakes. Although the summer season is short, it can be very hot; and this year the heatwave that began in early May has shown little sign of ending. But don't imagine that you can have a dip in any of the lakes marked on the map. The only point where bathing is allowed is Echo Lake, west of Somes Sound; otherwise, if you don't mind salt water, Sand Beach on the island's east coast is good for swimming, although it is often very crowded.

One of the most distinctive features of Acadia is its network of carriage roads, so called because John D Rockefeller Jr, who funded their building, wanted to be able to drive around in his horse-drawn carriage undisturbed by motor vehicles. Cars are still banned from these roads, which has made them popular with walkers, cyclists and riders, as well as cross-country skiers in the winter months. The carriage roads follow the landscape's natural contours, and are built of rock so that they blend in with their surroundings; but some people feel that they spoil the otherwise wild character of the Park.

They may be man-made, but the carriage roads are still a good viewing point for some interesting birds and animals, even though the rarer varieties may stick to the areas of more dense woodland. Acadia is a home for mammals of all kinds, and although a face-to face encounter with a black bear is rare these days, there are plenty of moose, chipmunks, skunks, snakes and many other species. The National Park Service encourages visitors to fill in observation cards when they see something particularly unusual, in an attempt to monitor the animal population within the Park.

My first hike into Acadia was a walk along the carriage road around Witch Hole Pond. I had hardly left the parking lot before I spotted a small, hut-like structure - it looked similar in shape and size to a tent, but it was made of branches and reeds. It appeared I need not have worried about being unable to recognise a beaver's nest - for this was undoubtedly what it was. And the ranger was right - as the sun started to set, the beavers appeared in the lake.