National City is about 10 minutes south of downtown San Diego on Interstate 5. Public transport from central San Diego is easy on the MTS Blue Line trolley — the 24th Street and 8th Street stations are both in National City, about half an hour from the Old Town and Santa Fe Depot in San Diego.
The closest major airport is San Diego International (SAN), about 15 minutes by car. The border crossing into Tijuana is another 15 minutes south on I-5 or I-805.