In The Church of Jesus Christ of Latter-day Saints (LDS Church), a temple is a building dedicated to be a House of the Lord, and they are considered by church members to be the most sacred structures on earth. Upon completion, temples are usually open to the public for a short period of time (an "Open House"). During the Open House, the church conducts tours of the temple with missionaries and members from the local area serving as tour guides, and all rooms of the temple are open to the public. The temple is then dedicated as a "House of the Lord", after which only members who are deemed worthy are permitted entrance. Thus, they are not churches (meetinghouses) but rather places of worship. The church is a prolific builder of temples as they hold a key place in LDS theology. At present, there are temples in many U.S. states, as well as in many countries across the world. Several temples are at sacred sites of the LDS Church, such as Nauvoo, Illinois and Palmyra, New York. The importance of temples is often emphasized in weekly meetings, and regular participation in temple work is strongly encouraged for all Latter-day Saints (LDS).