Where staying (or do you know) and how old kids?
Things I would definitely do:
Zoo
Safari Park
USS Midway
Balboa Park/Museums (by a pass for unlimited if they have it)
Beach (I'd probably do La Jolla, unless you're staying near another one)
OOPS, you said without kids
. I'd still consider these, but I'd be less busy with kids. Maybe Zoo/Beach/Balboa Park.
Depending on where you stay I can let you know restaurants. Little Italy is the best area to dine and full of great options.