Updated: Apr 9, 2021
If you want to enjoy the hole view of Bay Area and pacific side, I totally recommended Mt Umumhum trail, it is most highest mountain around Bay Area, if weather is clean, you can see Pacific Ocean and South bay area.
And there is popular landmark on top of Mt Umunhum, you can find the history of the building in below link.
Visible even from great distances, the so-called Mt. Umunhum Cube is a well-known landmark in the Bay Area. The Cold War era radio building was built in the early 1960s, but has been long since abandoned today. While in use, the five story building was used to keep an eye on the sky and look out for enemy aircraft that might have wanted to start not-very-chill air strike on the West Coast.
The Cube was left to rot in 1980 when the airbase that operated the station was decommissioned. Like many abandoned points of intrigue, the Cube has attracted its share of visitors over the years, but technically the site is off limits for safety reasons. Even if it is no longer used, the cube is still a haunting beacon atop the lush mountaintop. Those who have gotten to see the thing up close, have seen that all of the doors and windows are boarded up as well.
The Midpeninsula Regional Open Space District has revived the area, and the summit is now open to the public after decades of closure. Visitors are able to drive to the summit and park near the Cube, as well as enjoy new trails and a ceremonial space honoring the site’s Native American history.