They operate, maintain or repair geothermal power plants and commercial and residential geothermal heating installations. (googled this for you)
The Tower of London was built in the year 1078 by King William, Duke of Normandy.
This Tower is more than 1000 years old and is the oldest palace, fortress and prison in Europe. History tells us that King Edward of England failed to keep a promise to give his throne to William, Duke of Normandy but instead gave it to Harold Godwinson, his English brother in law.
William became angry and sent his army across the English channel to conquer England and on October 14, 1066 he fought with Harold and won the battle. Later that year on Christmas day, William was crowned King.
To keep the unruly citizens of London in line, he decided he needed a stronghold and so he built the Tower to act as his fortress.
With time, other smaller towers, extra buildings, walls, and walkways were added gradually transforming the original building into the splendid example of castle, fortress, prison, palace and finally museum that we enjoy today.
The Tower of London is a tourists attraction today.
The last option would be the best answer I think.
