One morning we toured the Old San Juan fort areas. These massive structures were built during the 1500s-1600s time period. To stand in an area where battled took place is quite outstanding. The beauty of these structures is truly remarkable and it was a beautiful day to take in these historical sights. 
We spent most of the morning at Castillo de San Cristobal. This Spanish fort was completed in the late 1600s to fight of land attacks on San Juan. It's older, more famous neighbor, Castillo San Felipe del Morro, was constructed to defend against water attacks and guard the bay area of San Juan. Here are a few interesting things I learned while visiting San Cristobal:
The Spaniards fired the first shot from this fort during the Spanish-American war in during the late 1800s. Below is a picture showing the main plaza area. The doorways lead into vaulted rooms where cannons were housed to fight of enemy attacks.
There are a series of several underground tunnels used to connect all the areas of the fort. This picture below shows the 3 tunnel entrances. These tunnels were used for several things; including moving men and supplies during battle, mining galleries, and the tunnel on the far left leads to the only dungeon at San Cristobal.
Three flags fly over Castillo San Cristobal - the Puerto Rican flag, the US flag, and an old Spanish military flag, known as the Cross of Burgundy. I love the picture below, the true beauty of this place stands out to me in this picture. The flags flying against the blue sky background, the rounded windows of the sleeping quarters for the soldiers, and the old original brick of the structure - quite a remarkable sight and part of world history.
Castillo San Cristobal offers a breathtaking view up the coast line towards it's counter part - El Morro. Below you can see the waves crashing against the sea wall and off in the distance, the watch tower of El Morro.
