By the middle of junior year, I started receiving 10-12 pieces of mail a week from colleges all over the country. Many prompted me to schedule a campus visit, so off I went. I've visited three colleges so far, but you should visit as many as you can if you are interested in attending because it is a great way to get a candid, casual feel of the place you may be living for two, four, or more years, instead of the formal feel of the college website or brochures.
Most schools will have an open house day or weekend when you and your family can come for campus tours, application seminars, and interviews with admissions counselors. They usually take place in the spring, when students are still on campus for classes; students usually lead the tours as well, so it is a great time to ask questions about the college from people who are attending it.