A great tour and well worth the cost. In total, it's about 90 minutes long and they run a group every 15minutes. We were surprised that many of the tours were booked solid on a weekday. You may want to make a reservation if you can't be flexible with days or times. However, even if the website says they are sold-out, you may want to drive up there and check with the bookstore if you've procrastinated. The tour goes inside to outside quite often (The architecture was designed this way on purpose), so you may want to bring some sunscreen and bottled water.