Tree houses are more popular than ever, as play spaces for children but also as luxury hotel (and even residence) designs for adults. Some of the most fantastic plans and ideas can be traced to specialist designers and builders — and pictures of their work can provide some of the best inspiration (as well as an informal visual guide) for do-it-yourself recreational, residential and commercial tree buildings.

Blue Forest is one such company, though they’re far from the only one. Based in the UK, this company seems to focus its specialties somewhere between playful little fantasy structures and big educational spaces for children engaged in wildlife observation, forest ecology and related nature-oriented pursuits. They’ve built a whole lot of these magical-looking buildings, and each one is unique, often designed specifically for the trees around which they’re constructed.

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The trick is often to find a balance between safe and fun – railings are a must, as are sturdy supports, but whimsy and asymmetry help make these places feel more organic and engaging for younger visitors in particular.

Some take on the character of a playground, with ropes, ladders and low elevations – or are more like the traditional club-house spaces we associated with ‘tree houses’ from our childhood.

Some are like mansions, fortresses or castles – just set up on stilts instead of sitting on the ground.

Still others (were it not for the color in the pictures) seem timeless or like they could have been constructed in the Middle Ages – until you reach their incredible contemporary interiors at least.

On the inside, Blue Forest tends to go for a combination of styles – modern simplicity with rustic natural wood-panel walls and floors with straw-infill wooden ceiling structures that feel like something between a rustic tropical resort hotel and modern rural house or home.

Aren’t these custom tree houses cool?