That's when Holland's famous flowers are in full bloom -- especially at Keukenhof Gardens in between Amsterdam and Rotterdam, where visitors can see more than 7 million flowers in their glorious rainbow of colors. Still, other Dutch and Belgian cities bring more delightful sightseeing in the springtime, and the passing landscapes that river cruisers view from their "floating hotel" are absolutely gorgeous. Here's a peek at some of the highlights of this region in the spring:

River cruises often start or end (or do both!) in Amsterdam, the capital of Holland. This waterfront city has an amazing history that dates back more than 700 years. It began as an important seaport and center for trade, and today Amsterdam beckons visitors to its incredible art and history museums, thriving restaurant scene and vibrant nightlife.

Water courses through Amsterdam in a network of canals spanned by more than 1,000 bridges. One of the most popular ways to get an overview of the charming city is on a canal tour. Glide along the waterways in a glass-topped boat past seventeenth-century gabled houses and colorful barges. Dinner cruises, happy-hour cruises and jazz cruises are other festive ways you can enjoy some time on the water in Amsterdam.

Museums are among the most popular attractions in Amsterdam. Most visitors take some time to stroll through the world-famous Rijksmuseum. It possesses an unrivaled collection of Dutch art, from early religious works to the Golden Age. Many masterpieces by Rembrandt are on display here, including his famous Night Watch painting of militia men. The Van Gogh Museum, housing more than 200 paintings and 550 sketches by the Dutch artist, is also located nearby.

The Anne Frank House, in the center of Amsterdam, is the hiding place where the teenage Anne Frank wrote her famous diary during World War II. Today, the rooms are empty, but still breathe the atmosphere of that period of time. Quotations from her journal, historical documents, photographs, film images, and original objects that belonged to those in hiding and their helpers illustrate the events that took place in the hidden annex. The original diary and other notebooks are on display here.

Once you board your river cruise ship to make your way through Holland's waterways, you'll dock at smaller towns along the way. Depending on your itinerary, you might visit Kinderdijk, with its collection of eighteenth-century windmills; Arnhem, home to the Dutch royal family's residence for 300 years and also a significant WWII site; Dordrecht, with its Grote Kerk, a church that dates back to the twelfth century; Zierksee, with a beautifully preserved medieval center; or Rotterdam, not really a "small" town, but actually the world's busiest port!

Perhaps the highlight of any springtime river cruise in Holland is a day-long excursion to Keukenhof Gardens. The world-famous park holds an exhibition of flowering bulbs annually; this year it's open March 19 to May 21, 2009. While the peak blooming time of the 7 million flower bulbs planted here is highly dependent on Mother Nature (and whether or not it's been an unusually cool spring), in general you can count on seeing some gorgeous hues of color in multiple rows of flowers when you visit in April.

This 70-acre park bills itself as the most photographed place in the world -- and it's really no wonder, since it's not only filled with a spectacular display of tulip fields, but also lakes, more than 150 works of sculpture art, greenhouses and, of course, at least one quintessential picturesque windmill. This is one attraction where you won't want to forget your camera. Framed, enlarged photos of the awe-inspiring sights at Keukenhof Gardens make amazing decorative souvenirs to remind you of your delightful vacation in the Netherlands in the springtime.