My wife and I have had pretty good success with Hop-on Hop-off tours over the years, and this one did not disappoint. We booked a two day pass, which in hindsight was probably one day too many. We ended up spending a full day at the zoo, so we would probably have been better served simply doing that on its own. A word of warning, the trolley stop in Bilbao Park is a hefty walk from the zoo entrance and you'll have to do it twice if you're catching the trolley at the end of the day. That piece of poor planning on our part aside, the trolley is a brilliant way to get a quick overview of the city. There are plenty of interesting spots to hop off and the live commentary was informative and entertaining. Each driver has their own version of the tour, so even you're taking the circuit for a second time the tour is still interesting. The trolleys ran frequently and they were very good about making sure they picked everyone up efficiently at the end of the day when some of the trolleys filled up. I would definitely recommend this for anyone looking to get a great overview of San Diego and its history.