The Balboa park downtown is wonderful, the marinas of course. The "wall" and the long lines at the border. Lots of interesting people shots at the border. (Though I would clear it with the border patrol folk first.) Also GasLamp Old Town is interesting.

Tijuana Slough wildlife refuge (No. It is still in the US, a few miles north of the border.)

Drive along hwy 94 and take the Tecate road. Even if you don't go to Tecate--though no reason not to--there are a lot of photo ops. Or over to Jacumba. Or you could take hwy 905 and cross into Mexico to go to Tecate via hwy 2D to hwy 2. That's very interesting and will give you an idea of the "maquilladoras" that NAFTA has created.

The media has latched on to the public fear and people think that Mexico is dangerous. But unless you are in the drug trade or law enforcement, it is really safer than living in Portland or Boise or Philadephia.

I love San Diego. I've considered moving there but would have to start my counseling practice all over--not a great option. San Diego is very diverse, lots of industry, recreation, Navy bases, some nice parks, great beaches. A lot of corruption in government. (They had three mayors in a row indicted one year. The fourth was a woman who tried to bring good government and some of her reforms have lasted.

The Maritime Museum. The Star of India, which is a sailing ship. There are several opportunities to take a boat tour on the bay. San Diego is a great place, and I'd live there myself if I had a chance! Someone suggested the para gliders along the Torrey Pines state beach, just a few miles north of the city. (I think that nudist beach is below the cliffs where they paraglide!) You won't run out of things to photograph, or to do or see! Others have made great suggestions. Balboa Park will have enough stuff to keep you busy for a day or so just by itself. I live about 2 hours away, and love it down there!

I see you only have a single day and you don't say if you have a car.

The above suggestions are a very good start. If you do the Embarcadero (waterfront), the Midway or the Maritime Museum and some shots of the Star of India followed by lunch in Old Town and the afternoon in Balboa Park, you'll have enough shots in the camera to be thinking of dinner downtown and some night pictures of the Santa Fe RR station. This is at the west end of Broadway and close enough to revisit the Embarcadero again or you could try Little Italy if you still have any energy left. This would also be a good choice for dinner. I've lived here for thirty years and if you give me more precise ideas of your likes and energy I may be able to help more. Email me if you like at robshipley@gmail.com

The above suggestions are a very good start. If you do the Embarcadero (waterfront), the Midway or the Maritime Museum and some shots of the Star of India, Old Town and Little Italy are close. Allow at least half a day in Balboa Park - the whole day if you want to do the the Zoo which is next door. If you're staying downtown some night pictures of Horton Plaza, the Santa Fe RR station, the Embarcadero and Seaport Village would be well worth considering. This is all at the west end of Broadway and close enough to revisit Little Italy again. This would also be a good choice for dinner.
Then further afield are mountain hikes, the Wild Animal Park, sunsets from Mount Helix and more. I've lived here for thirty years and if you give me more precise ideas of your likes and energy I may be able to help more. Email me if you like at robshipley@gmail.com