Hoover Dam, Nev.

In recent years, countries have been coming up with new and innovative ways to generate energy. The UK is currently constructing the world's biggest fat-fueled power station, set to produce 130 gigawatt hours a year of renewable electricity--enough to run 39,000 average-sized homes, according to the BBC. But while new power plants are being constructed, there are some standing today--from a geothermal power plant in Iceland to a tidal power station in Canada--worth touring. Some are burrowed into mountains, others were built underground, all are considered amazing feats of engineering and architecture.

On October 9, 1936, the Hoover Dam, harnessing the power of the Colorado River, began sending electricity over transmission lines spanning 266 miles of mountains and deserts to power the homes of Los Angeles. Today, it generates, on average, about 4 billion kilowatt-hours of hydroelectric power each year for use in Nevada, Arizona, and California--enough to serve 1.3 million people. The Hoover Dam holds Power Plant and Dam tours for visitors and they include guided tours of plant and the passageways within the dam itself and admission to the Visitor Center. The tours, which also feature audio and film presentations and exhibits, provide a comprehensive view of the massive dam and its operations, and the unique features around the site.

NEXT: A geothermal power plant on a volcanic ridge

Hellisheidi Geothermal Power Plant, Iceland

Located on an active volcanic ridge, tourists may not be too eager too visit Hellisheidi Geothermal Power Plant, the largest geothermal power plant in Iceland. But a volcanic eruption is unlikely in the Hengill area, where the plant is situated. Only three volcanic eruptions have occurred in Hengill in the last 11,000 years, the most recent being 2,000 years ago. With its high concentration of volcanoes, Iceland has an advantage in the generation of geothermal energy, the heating and production of electricity. During winter, pavements near areas such as Reykjavik and Akureyri, are heated up. This causes heat to rise to the surface. Hellisheidi, owned by Reykjavik Energy, is one of five major geothermal plants in Iceland. Today, it's considered one of the best showcases of geothermal power generation in the world, according to ThinkGeoEnergy. The power plant features a Visitors Center, which also holds an exhibition on Geothermal Energy. The center provides multimedia presentations on sustainable green energy as a global energy source, as well as the origins of geothermal energy.

NEXT: The only tidal generating station in North America

Annapolis Tidal Station, Canada

The Annapolis Tidal Station is a tidal power station located on the Annapolis River immediately upstream from the town of Annapolis Royal, Nova Scotia, Canada, and is the only tidal generating station in North America. Although tidal power is not yet widely used, it has a bright future in electricity generation, as it is more predictable than solar power and wind energy. The Annapolis Tidal Station, completed in 1984, was a government pilot project initially designed to explore harnessing energy from the sea. It harnesses the tidal difference created by the large tides in the Annapolis Basin, a sub-basin of the Bay of Fundy. Today, the Annapolis Tidal Station contributes 20 MW (mega watts) to the electricity grid. It currently houses a seasonal centre, where visitors can learn about the generating station, its history and the power of the Bay of Fundy.

NEXT: An underground power station in Scotland

Cruachan Power Station, Scotland

Nestled in some of Scotland's most spectacular scenery and buried one kilometre below the ground, the Cruachan Power Station is one of the country's most famed engineering achievements. Cruachan is a pumped storage hydro power station, opened in 1965, which can produce electricity for the grid in two minutes (or 30 seconds if its turbines are already primed on "spinning reserve"). Located in Oban, the station was built into a hollowed-out rock of a mountain, Ben Cruachan. It uses electricity from the grid at times of low demand to pump water from Loch Awe, to its storage reservoir part way up the mountain. The station houses a Visitors Centre (open from February to mid-December), which offers guided tours of the site. Once inside the mountain, visitors are taken up a walkway, past sub-tropical plants that grow well with the warm humid conditions inside the mountain, and then on to the visitor's viewing gallery. There, visitors can view the generating hall that houses the four generators that the station uses to produce electricity from water.

NEXT: A power station built 700 m inside a mountain in Norway

Sima Power Station, Norway

One of the largest hydroelectric power plants in Europe, the Sima Power Station's main hall is tunnelled 700 metres inside a mountain. The facility Lang-Sima operates at an installed capacity of 500 MW, and has an average annual production of 1,212 GWh. The facility Sy-Sima has an installed capacity of 620 MW, and an average annual production of 1,640 GWh. The power plant, operated by Statkraft, exemplifies Norway's expertise in the area of building and operation of hydroelectric power plants. The country produces 98-99 percent of its electricity from hydroelectric sources. According to the International Energy Agency (IEA), Norway was the 6th biggest hydropower producer in the world in 2008 after China, Canada, Brazil, United States and Russia. The Sima Power Station is open to visitors the middle of June until the middle of August. A guided tour features a 30-minute movie about the construction of the plant and a 30-minute walk inside the station hall.

NEXT: A spiral tunnel takes you down this power station in New Zealand

Manapouri Power Station, New Zealand

An underground hydroelectric power station on the western arm of Lake Manapouri in Fiordland National Park, in the South Island of New Zealand, Manapouri Power Station is the largest hydroelectric power station in New Zealand, with an 850 MW installed capacity. Its also considered one of New Zealand's greatest engineering achievements, with the majority of the work completed underground in a remote location. The power station machine hall was excavated from solid granite rock 200 metres below the level of Lake Manapouri. Access to the power station is via a two-kilometre vehicle-access tunnel which spirals down from the surface, or a lift that drops 193 m down from the control room above the lake. Visitors to Manapouri can take a cruise of Lake Manapouri (many companies offer a picnic lunch option) and a tour of the power station, including a trip down the spiral tunnel to the underground machine hall, where they learn more about how the station can harnesses the energy of rushing water to generate electricity.

MORE ON WEATHER.COM: World's Strangest Beaches