Earth > Europe > Northern Europe > United Kingdom > Gibraltar
Go to the border and just stand somewhere nearby; cars will be moving slowly. Be careful not to hitchhike too close to the border as there are many Guardia Civil (police formed by Franco) and they are not really kind to hitchhikers.
Try hitching at Europa Point! There are many tourists who are at least drive you back to the city centre. We got lucky and got a hitch further to Tarifa with the first car we asked!