Mainau; An enchanted garden isle in a region of quaint little towns

Standing by the ancient harbor of the island city of Lindau, one can look over the wide blue expanse of Lake Constance and see the mountains of Austria on the left and those of Switzerland on the right. If the day is particularly clear , the snowy peaks of tiny Liechtenstein also come into view.

But aside from spectacular vistas that give one the rare opportunity of gazing at three countries while standing in a fourth, the German side of Lake Constance has much to see within its own borders. Charming medieval towns and villages cling to the miles of shoreline as they have done for over a thousand years. Beautiful small islands, one of them the subtropical garden paradise of Mainau, invite exploration.

The small island city of Lindau is a good place to be based while visiting the area. Lindau, on the northeast corner of the lake, spent the first 10 centuries of its existence as a trading center and has quite successfully spent the last century as one for tourism. Two bridges connect the island with the mainland: one for cars and pedestrians; the other for the railroad, which runs frequent service with connections to other European cities.

Its hidden courtyards and narrow, twisting streets clearly establish Lindau as a city built well before the days of automobiles, and happily there are ample parking lots on the outer rim of the island where cars can be left. In the heart of the old city many of the streets are open only to pedestrians, a situation that makes shopping and strolling all the more pleasant.

Lindau possesses many venerable and carefully preserved buildings. But there is an even earlier antiquity to be enjoyed in the village of Meersburg about 30 miles to the west. Some of the most charmingly crooked half-timbered houses to be found anywhere line the narrow streets rising steeply from the lakeshore below.

Even the half-timbered houses, dating back 500 years or so, are new in comparison with the Old Castle of Meersburg, a fortress with moat and dungeon. One enters the castle -- it dates from 628 and is the oldest in Germany -- where the original drawbridge once was lowered, crossing a ravine that overlooks a medieval mill with a huge water wheel turning in the waters below.

Down a steep hill from the castle and the old section of Meersburg is what villagers call the ''lower town,'' an area of turn-of-the-century hotels and sidewalk cafes lining a flower-decked promenade along the lake. From the lake front of Meersburg ferryboats make frequent trips to the town of Konstanz on the opposite shore.

What lures many visitors, 2 million last year, into making the trip is a spectacularly lovely garden park called the Isle of Mainau, which lies on the western edge of Konstanz. Connected to the mainland by a slender causeway, Mainau is the property of Swedish Count Lennart Bernadotte, who has tended it since 1932.

What you see at the Isle of Mainau depends very much on what time of year you are there. Open from April until the end of October, the terraced gardens and lush hillsides overlooking the lake bloom with an ever-changing blanket of color. On the island's highest vantage point is Count Bernadotte's baroque palace and an exquisite rococo chapel, which is open for tour. Adjoining the building is a conservatory of orange trees and cascades of colorful orchids.

When the park opens in April, visitors are treated to meadows of tulips and daffodils which flank each side of Spring Street. Some 600,000 new bulbs are planted each autumn, many the newest varieties available, to assure an extravaganza the following spring.

Next to bloom are 280 varieties of rhododendrons, which frame many of Mainau's meandering stairways and paths. In June the rose garden, the acknowledged highlight of the island, comes into glory. The rose garden, a stylized area of terraces, archways, trellises, and statuary, is the island's most elegant feature. Despite the formality of the setting, many of the huge rose bushes and trees are actually wild plants that have grown on the island for over 500 years.

During summer Mainau enjoys a subtropical climate that allows it to harbor vegetation more commonly found along the Mediterranean. Palm trees, cypress topiaries, lemon trees, and even banana trees can be found along the lush avenues encircling the park. The weather also is mild in fall, the season when brilliantly colored dahlias are resplendent in the south garden.

But where Mainau's horticultural artistry reaches its peak is in the area called the Children's World. Here you will find at least as many adults as children enthralled by the three-dimensional plantings of animals and other figures. Among these fantastic plant sculptures is a giant parrot planted with blue pansies and a sea rabbit, a legendary creature said to have inhabited Lake Constance, fashioned out of white pelargoniums.

Although Mainau has been famous as a garden park for only about 50 years, its origins can be traced back 2,000 years when the Romans

used it as a strategic stronghold. It is apparent that the island, along with the rest of Lake Constance, has managed to grow more beautiful with age. Practical Information:

The closest major airport to Lindau is in Zurich, about an hour by train. The next closest is in Munich, about 21/2 hours by train. Getting around in the Lake Constance area is easily done by car, but the most scenic tour is by boat. A tour-boat service known as the White Fleet carries passengers between many stops along the lake, including Lindau, Meersburg, Konstanz, and the Isle of Mainau. The address of the Lindau Tourist Office is Verkehrsamt, Bahnhofplatz, 8990 Lindau, West Germany.