A day trip in Gibraltar is great. Park at La Linea and walk across customs. You get the fun experience of looking both ways as walk across the airport tarmac. It's easy to hire a taxi tour if that is your choice to drive you around. We took the bus from tarifa to spend the day at Gibraltar. We were based in Tarifa, as the following day we were taking the ferry over to Tangier to spend 5 days in Morocco.