The world-famous and utterly majestic First Church of Christ, Scientist was built in 1894 by the original Christian Science congregation (led then by the denomination's founder, Mary Baker Eddy) and expanded in 1910. Its stunningly beautiful chapel incorporates Byzantine and Roman architectural elements and houses the 8th largest pipe organ in the United States (with more than 13,000 individual pipes). Guided tours are available five days a week. A tour lasts about 25 minutes and is free.