What are some fun ideas for senior citizens in San Francisco that don't cost a fortune for June/2014. Anyone done the duck bus tour?

Quantify "fortune".

And how spry are the seniors in question.

Age 65 or 80?

70 year old plus friends due in town this week...one with atrial fib and another not feeling well in general...Not so spry these day, but not using a walker...No idea what their budget is either...Ideas?

These are great. They are free - donation only [$5 to $10 is what we do, depending on how many we plan on doing] - and sponsored by SF Public Library [money goes to organization, not the guides]. There are dozens of tours covering almost every taste and like. We have done over 3 dozen of them over several visits.

http://www.sfcityguides.org/