I have a 12 month old and we only go to playgroup on a Wednesday and Storytime at the library on Thursday (not that she even notices stories are being read! The first week she bounced on my leg the whole time, and last time she crawled over to the kids books and kept taking them out of the boxes on the floor but it's still good for her to be around other people I guess).

Does your local library have any programs like that you could go to? Even just going to the park and being around other kids will provide stimulation.