Mormon temples are beautiful architectural additions to any city they are in. When Mormons arrived in Salt Lake City in 1847, the first thing Brigham Young did was to mark out the temple site. The whole city was designed around it. This was partly because the temples the Mormons had previously built in Kirtland, Ohio, and Nauvoo, Illinois had been destroyed by angry mobs. Building a new temple was a sign that this was a place that Mormons believed they would be able to stay long-term, that the Lord had promised them safety here.
Other temples in Utah were actually completed before the Salt Lake Temple, because of the unique care that went into its construction and it remains the iconic temple for many Mormons and non-Mormons who visit Salt Lake City.
Until the twentieth century, there were only temples in Utah and Mormons from other countries had to find the funds to travel to Utah, which was very costly, in order to go through temple rites necessary in Mormonism for salvation. But now there are currently 149 temples worldwide (with about 25 others in various states of construction). Some of the temples are very small, built in conjunction with chapels, and are to allow the Mormons who live in the area the chance to return to the temple often and renew their covenants. But it's not always clear to non-Mormons what goes on in Mormon temples and why Mormons would also then have churches, as well.
Mormon churches are the space Mormons use for regular Sunday worship meetings. Like many Christian churches, Mormon churches have a chapel for communion services (called "The Sacrament") in the center and classrooms circling around the chapel for Sunday School, women's meetings, priesthood meetings, and children's classes. There are also often kitchens for warming food for many events, anything from a Boy Scout meeting to a graduation celebration or a funeral or wedding reception, often on weekdays. There is even a "gym" that is used for basketball or volleyball practice for church teams and which can be converted with tables and chairs for a potluck.
Nearly every Mormon church also has a baptismal font (with warm water!) for live baptisms with a changing area connected to it to make it convenient for multiple baptisms of eight year-old children that often happen one day a month. Some Mormon church buildings are "stake buildings," which means they are designed beyond a single ward (or congegration). In these buildings, there is space to house the Stake Presidency offices and the chapel is often large enough, and built with overflow areas for stake meetings. There is a nursery with toys for young children while their parents worship and a mother's lounge for women who are more comfortable nursing babies away from others.
Mormon temples, on the other hand, are not used for regular Sunday worship and are usually closed on that day. Mormon temples exist because of the Mormon belief in a responsibility to ancestors who did not have a chance to hear about Christ or to choose baptism. We believe these ancestors may be waiting for these rituals to be done in order to be allowed with their own families. Sealing together married couples and families both living and dead is part of the great work of Mormonism.
Some of the rituals that can only be performed in Mormon temple include:
1. Baptisms for the dead.
2. Weddings and marriage sealings for eternity.
3. Endowment ceremonies.
On the lower level of the temple, there is a "Baptistry," where twelve stone oxen hold a basin of the water to symbolize the covenant twelve tribes of Israel, which Mormons believe they are spiritual descendants of. This is where baptisms for the dead are done, and it is the only place in the temple Mormon youth (ages twelve to eighteen) are considered old enough to attend--if they are worthy of a temple recommend. If you are interested, here is a link that shows some photos of the interior of the temple rooms.
On the main floor of the temple, there is a "bridal room" where a bride can put on her wedding dress and have a few special people with her to guide her through the big day (and the groom, as well, has a special space and guides to help him--usually a father who is designated with a specially colored tag to make everything clear and efficient).
Above the main floor, there is a sealing room with a marriage altar and mirrors on either end to symbolically represent the eternities that this marriage will last, and an altar where very simple Mormon vows are recited. (There is not "I do" in a Mormon wedding ceremony, just one simple "Yes.") Mormon weddings are usually quite small and because they require all attendees to hold a recommend, sometimes can exclude family members, which can cause some hurt feelings. Families members without a temple recommend are invited to a special waiting room and can participate in all the photos outside the temple, which is the only place photography is allowed.
The celestial room is the center of every Mormon temple, and is often a beautiful, very quiet room with a crystal chandelier in the center, stained glass windows, and with beige or very light-colored couches and other chairs. This room represents the celestial kingdom, or the highest level of Mormon heaven. Mormons reach it after they pass through the work of the endowment ceremony either for themselves or for deceased ancestors. It is a place of contemplation, peace, and often divine revelation. Here is an official link about ordinance work in the temples.
Once a temple has been dedicated, only those who hold a temple recommend can go enter its doors. There are temple workers stationed there who check the passes (now electronically coded). The temple recommend requires an interview with a bishopric member and a stake presidency member and there are numerous questions, designed to ensure that only the faithful and most worthy enter the temple. Some include questions about following the Word of Wisdom (the health code that determines Mormons should not drink or use tobacco, for instance), about not being involved in spousal or child abuse, paying proper child-care payments, and belief in basic tenets of the church. Members are also asked if they consider themselves worthy.
I think the reality that most religions do not have an equivalent of the Mormon temple is part of the reason that it has become an object of so much speculation--even the ridiculous claim that sacrifical blood rituals are being performed (they aren't). Temples are sacred spaces to Mormons, who have done work worldwide to gather genealogical records to help join the human family together. If you are interested in your own ancestors, you can get free information about them here. Last year, the Mormon church released information about millions of African slaves brought to America whose names, birthdates, and other information were not previously available.
Many Mormons spend years studying the lives of their ancestors before they do temple work and they find great meaning in the experience of drawing close to them in the temple. Mormons believe that the spirits of these ancestors may prod on their work, guiding them to certain important pieces of information or artifacts, and that these ancestors may also be present while their temple work is being done. However, no Mormon believes that any spirit is forced to believe in Mormonism in the after-life through these rituals. Mormon temples may seem expensive and extravagant, but they are built both to glorify God and for the practical work of sacred rituals for us and our eternal families.