Following the GPS coordinates of the "Pete's Castle" Geocache led us to this old castle like
tower in Palo Alto.

From the description from the Geocache page :

This tower was built in 1875 by a mysterious Frenchman named Peter Coutts who owned the 1400-acre Matadero rancho. Peter Coutts is now supposed to have been a Frenchman named Paulin Caperon who was a retainer of the exiled Empress Eugenie, widow of Napoleon III. On arrival here, Coutts began the construction of a large estate, based on buildings at Versailles, for which many buildings were planned - only one was begun – along with a strange tunnel complex. Peter Coutts was always evasive about his circumstances and all his monetary dealings were done in the name of his children’s governess. It isn’t certain how many tunnels there were but most say there were six. The tunnels were supposed to have been created to supply water to the estate and farm. Many contemporaries felt that the tunnels were far to large for that. Fueled by Peter Coutts’ mysterious demeanor, rumors flared. The tunnels may have been built to amuse Empress Eugenie (said to be fond of the clandestine). They may have been a hiding place for his fortune (believed stolen from the French government). They may have been a hiding place for Mr. Coutts himself built to avoid government agents chasing him, with the tower as watch post and fortress for a siege. Adding to the great mystery of the Frenchman’s Tower was the fact that after six years living and building in Palo Alto (Mayfield at the time) Peter Coutts disappeared. About one year after he disappeared Peter Coutts was back, many thought reclaim his gold from the tunnels under his land. He did not stay long and soon after he sold the land to Leland Stanford, then governor of California. Over the years many people have searched the tunnels for treasure or some answer to the mystery of there existence; nothing was ever found…

The following website is the Geocache page:
http://www.geocaching.com/seek/cache_details.aspx?guid=64ce66f8-46c2-4e1b-af08-1d1ae8a3d66e