Royal Greenhouses of Laeken, Belgium

The Royal Greenhouses in Laeken are normally reserved for the Belgian royal family, but luckily during three short weeks in spring, the general public gets a chance to enjoy this architectural and horticultural treasure. Needless to say, it's a popular tourist attraction, so expect to bump elbows with a few other interested visitors.
The whole greenhouse complex covers an impressive 2.5 hectares (270,000 sq ft) and is made up of no less than eleven interconnected glasshouses. There are several large greenhouses, two major domed buildings with beautiful cupolas, and a long glass walkway that snakes across the rolling landscape. The whole monumental complex is literally a "glass palace", with some greenhouses being used for state receptions, and one of the domed greenhouses known as the ‘Iron Church’ originally conceived to serve as the royal chapel. The whole complex was designed by Alphonse Balat, Victor Horta’s teacher.

In addition to the impressive architecture, the complex houses a large collection of plants, from camellias, to clivias to palms. However, I think the most impressive plants are the tree ferns. There must be hundreds of them, all beautifully set in lush arrangements with many other ferns, greenery and flowering plants.
Also very impressive are the geraniums and fuchsias. The entire interconnecting walkway greenhouse is completely covered in blooms: six-foot high geraniums along the walls, and tree-sized fuchsias smothering the ceiling. A unique experience, but be prepared for long line-ups and many unavoidable strangers in your pictures.

Garden Summary
What: Royal Greenhouses of Laeken, Belgium
Where: Brussels, Belgium [Map].
When: Only open for 3 weeks in spring, around the middle of April to beginning of May. Different opening hours each day, so check the website and time your visit carefully. There are many, many visitors, so if you want to avoid impossibly long line-ups, get there before the opening times. Otherwise, it's basically one long packed stream of people slowly snaking through the complex.