I couldn't just stop a stone's throw before the Mexican border, after having crossed the Canadian/USA border two month ago. To complete it, I rode the remaining 35 km from San Diego on my last day. Tijuana is the first city right after the border.
Crossing the border in one direction was easy. There was not even a passport control. I took my bike with me, after having heard very different recommendations about whether to lock it on the other side of the border or better not leaving it anywhere unattended. Thus, I had more time to see other parts than just the main street, where there's a lot of tourist traffic going on. The best encounter, after uncountable "Hey, buy these cheap necklaces" calls after walking only two blocks, was a father with his daughter (around 20), asking me what I'm doing here alone. We talked a little, and I asked them where they would recommend me to eat something real Mexican. They described the way to a Tamales place (interesting stuff wrapped in corn or banana leaves) some blocks off the main street. And then they even offered to take me there! So they took me there and helped me ordering (everything was in Spanish) and I just followed their recommendations, which was much better than just going to some random place on the main street. They were so helpful and made my very short Mexico experience worthwhile (don't know if this is the correct word).
Crossing the border in the other direction was different. A long line of pedestrians and a much longer line of cars made their way through the passport control, it took approximately 45 minutes to get back.
I had planned to take a different route back to San Diego, but it would be dark within one hour, so I took the commuters train. It's very similar to the aboveground underground trains in Frankfurt.