In the town of Harads - about 50 kilometres outside of the city of Lulea in northern Sweden - there are five "invisible" cubes hanging in the trees. The cubes are part of the innovative Treehotel and were built and function with environmental, eco-friendly and non-invasive materials and systems, thus co-existing with their natural surroundings. The most iconic of the rooms is 'The Mirrorcube', which is clad in mirrors that reflect the trees around the structure while concealing it from the natural world. To cover all their bases and ensure that the presence of 'The Mirrorcube' did not disturb local wildlife, the designers covered the walls with infrared film - invisible to humans but highly visible to birds. The hotel also hosts retreats - sign us up!