The great siege tunnels is a great place to visit for history buffs and everyone else because you will able to understand importance of Gibraltar as a key military location. Tunnels are about 1 mile long and it took us about 1.5 hours to go thru. We took a lot of stops to read the posters and to take pictures from the portals in the walls. You don’t really need an audio guide since posters provide the same info in English and Spanish. As an added benefit of the tour you will see aerial views of Gibraltar and learn how tunnels were carved out.