For the Spain they believed to be better:
in Campo de Gibraltar
Operation Felix was the codename for a proposed German seizure of Gibraltar during World War II, subject to the co-operation of Spanish caudillo Francisco Franco It never went ahead, chiefly because of the supposed Franco’s reluctance to enter the war.
The fortification of the Strait of Gibraltar during the 20th century was one of the main projects carried out by the Franco regime in the first years of the postwar period to guarantee the stability of the border between Spain and Gibraltar. After the end of the Civil War the newly created Spanish government had as a priority to guarantee the integrity of its borders before possible attacks mainly after the fall of the fascist and National Socialist regimes of Europe. To protect these borders, a system of fortifications based on anti-tank bunkers and machine-gun nests similar to that created in other parts of Europe was created. According to the mentality of the time, the best way to fortify a border area was the construction of different lines of defense formed by bunkers with anti-tank artillery and machine-gun nests.
On the other hand, the tunnels of Gibraltar, constructed over the course of nearly 200 years principally by the British Army, have made the rock Rock of Gibraltar "a veritable warren of tunnels that housed guns, hangars, ammunition stores, barracks and hospitals".
When World War II broke out in 1939, the authorities from Gibraltar evacuated the civilian population so that the military could fortify Gibraltar against a possible German attack. By 1942 there were over 30,000 British soldiers, sailors, and airmen on the Rock. They expanded the tunnel system and made the Rock a keystone in the defense of shipping routes to the Mediterranean. The total length of the tunnels increased greatly during the war, from 11 km to 40 km.
The tunnels accommodated what amounted to an underground city. The entire 16,000-strong garrison could be housed there along with enough food to last them for 16 months. Within the tunnels there were also an underground telephone exchange, a power generating station, a water distillation plant, a hospital, a bakery, ammunition magazines and a vehicle maintenance workshop. They also housed one of Gibraltar's most secret places – Stay Behind Cave, built for Operation Tracer, a plan to maintain a secret observation post manned by six men within the Rock if it had fallen to a German invasion. It was not rediscovered until as recently as 1997.
These photos were taken in April 2018 and show one of the bunkers in Sotogrande (San Roque, Campo de Gibraltar), one of the World War II tunnels in the Rock of Gibraltar, and the Rock itself seen from Ceuta.