When we head out...
On days when my husband heads out for a business trip, I try to find activities outside the house to help me keep from going insane. Some of the typical places include many of the local parks(open spaces) & libraries. Here on the mid-Peninsula there are many options that sound really appealing for parents trying to get out of the house. Some are free and others have a fee for entry or membership.
Rancho San Antonio
Hidden Villa Farms
Stanford University(Lake Lagunita, Cantor Art Museum, etc.)
Palo Alto Jr Museum & Zoo
I'll get links and write up some thoughts on kid & parent friendly reasons why I like these places. Of course there are a ton of indoor bounce house locations and places like MyGym/LittleGym but it takes my kids a long time to warm up to these drop-in play places with such a limited time, it didn't feel worth it.