As a member of the Church of Jesus Christ of Latter-day Saints, I attend the temple as much as possible. If you've ever been to Utah, seen pictures of Salt Lake, you've probably seen a Mormon temple. Even if you haven't, you might have seen on anyway, because they're becoming more common all over the world. I currently attend the Provo, Utah temple, as it's just a short walk or drive away from BYU. I have been inside the Boise, Idaho; Washington, DC; Salt Lake, Utah; and Rexburg, Idaho temples to do baptisms for the dead and have stood on the grounds of many others. A temple was dedicated this summer in my home town of Twin Falls, Idaho. I had the great opportunity to attend and help out with the open house (spoken of briefly below).
The temple is the house of God. In fact, on every temple, cut into the stone is the phrase "House of the Lord, Holiness to the Lord." Only faithful members of the Church can go inside, although before a temple is dedicated there will usually be an open house for the general public to take a look inside. The temple is a place where we can be close to our Heavenly Father. We learn of him and what he wants for us. In the temple, a couple can be married not only for time, but for forever. We believe that families are eternal, and it is through the temple that this happens. The temple is where sacred ordinanaces are performed, both for the living and the dead.
Although I haven't been through the temple to have my own ordinances performed yet (I most likely will in a few years), I have been in the temple to do baptisms for the dead. Baptism is a key to salvation, and so everyone must be baptized, but some people did not get the chance to hear about the gospel on the earth. In the temple, members (usually young people, ages 12-20sih, although it can vary) are baptized in proxy for the deceased, who then have the chance to hear the Gospel and accept it in the spirit world.
Today I had the opportunity to go do baptisms in the temple with two of my friends. How wonderful! To sit in the dedicated building, feeling the spirit of God, and receiving revelation for what He wants for me, and also to serve those who came before me but didn't get the chance to hear the wonderful message of our Savior Jesus Christ.
Here is a link to a video explaining more about the temple and also showing some clips from the interior of the Twin Falls, Idaho temple: http://www.magicvalley.com/articles/2008/07/12/features/religion/140207.txt (Note: Pictures aren't taken inside the temple after it's dedicated. This video was taken before the dedication as part of the open house). Also, the picture at the top is of the temple in Twin Falls as well.