There was a time when the expression "ecological hotel" evoked images of a lodge in the tropical forest, empty of electricity. These days are far behind us. Today, green hotels are among the most stylish - and even the most user-friendly - thanks to innovations in design and technology, and the growing demand for sustainable options. To imagine what the future might look like, we went around the hotels that are pushing the limits of what is possible. Here are six of them that have gone around the world stunningly, but also visually and in the ecological department.

Villa Awang Awang Awang, Bali

This property in Bali is not what most people consider ecological - it is a luxury villa - but the environment is beautiful, and the hotel's green features help to keep it that way. The hotel is located on the side of a ravine overlooking the Petanu River, which provides hydroelectric power to the hotel. Its design catches cross breezes, minimizing the need for air conditioning. Wastewater from sinks and showers is reused in the hotel garden and food waste is composted or given to village animals.

Hilton Fort Lauderdale

Standing in front of the Hilton Fort Lauderdale, visitors will notice something striking: six 52-foot high wind turbines on the roof of the 25-storey hotel. The turbines were installed in 2014 - the first of their kind for a hotel in the Americas - and would produce enough electricity to keep the lights on in the 374-room station throughout the year.

Hyatt at Olive 8, Seattle

Virtually every part of the Olive 8's design is environmentally friendly, from low temperature plumbing fixtures, to all-glass exterior (which reduces the need for fixtures), to painting on walls. In fact, this Seattle hotel is one of the few LEED Silver certified hotels in the United States. But the most impressive - and visibly sustainable - offer of the property could be the green roof. The 8355 square foot space has more than 25,000 sedum plants, chosen because they do not require much water. It also helps to reduce storm-water runoff by absorbing rainwater and helps to lower temperatures.

Hotel Milano Scala, Milan

Hotel Milano Scala guests should not feel guilty about using air conditioning. The 19th century building that houses the character property is equipped with a heat recovery system: the hot air generated by the air conditioning is used to heat the hotel's water. This technology - although not very visible to visitors - made Milano Scala the first zero-emission hotel in Milan when it opened in 2010. The roof garden even provides herbs and vegetables for La Traviata, the ground floor restaurant.

Arenas Del Mar Beach and Nature Resort, Costa Rica

Nature is the main attraction at Arenas Del Mar Plage and Nature Resort, a 38-room luxury complex located five minutes from Manuel Antonio National Park. The park is one of Costa Rica's most diverse ecosystems, and virtually all hotel visitors encounter monkeys, lazy people and lizards. Peaceful coexistence requires careful planning. The developers even studied the native animals and built the hotel to minimize interference with their habitat. The electrical system operates underground, for example, and trees have been included in the roofs of some buildings to avoid having to cut them down.

Hoshinoya Karuizawa, Nagano

Since 1914, people have been travelling to the hot springs of Hoshinoya Karuizawa, an isolated mountainside resort. Located in Nagano, Japan, the property is located in a beautiful landscape with panoramic views of the woods. It also harnesses the power of nature: the resort and its thermal bath are powered by the geothermal energy of Mount Asama, an active mountain. The rest of its electricity is generated by mountain streams.