I believe there are various walking tours offered, but the one I did was basically a pub crawl of four breweries and sampling a wide range of Mexican craft beers. The guide, Andres, was friendly and knowledgeable. The best way to sample as many beers as possible is by ordering 'flights' - smaller glasses of four beers of your choice. Tijuana is an interesting town, worth a visit. it only took about 10 minutes to get into Mexico, but an hour to get back into the US, but that was on a Sunday evening which Andres said is a very busy time, so not too bad really. Then it's a 45 minute trolley ride to American Plaza in downtown SD.