The stately houses along the canals and streets of central Amsterdam may seem crammed together, but the houses have spacious rear gardens that are not visible from the outside. Many gardens are joined, creating vast green spaces peppered with huge trees, flower gardens, garden houses and ponds. Every year Amsterdam's Canal Museums organise Open Garden Days so that visitors can discover the hidden beauty behind the canal-house facades. Around 30 gardens - including many private gardens - will be open, and this year the theme is colour. The only access is usually via the house, so visitors also get a peek inside these special homes.