Mount Diablo Summit Museum at Summit Road, Walnut Creek, California.

Great for people who are challenged mobily. You can drive all the way to the summit and if they're able to go up some stairs see some great views. Even if you are not able to walk up stairs or mobile, you will be able to stay in the vehicle and still see a lot of the view from the top.

During the winter it can be extremely cold, so make sure to dress appropriately for 30 to 40 degree weather. As a matter of fact it's snowed the last time I was there in late March.