I suppose all your local tours of museums and historic houses etc are too lightweight? I often sign up DD for holiday programs for 13+ year olds, maybe an art history class at the gallery, or something like a naval history museum? Libraries often have heritage events, and we occasionally go to free public lectures at the universities.
Another thing I do is keep an eye on the events listings for the local homeschoolers, they very often organize unusual but interesting outings and don't mind DD and I tagging along. DD's teacher is fully onboard with me sneaking her out of school every couple of months to go do something more worthwhile and I'm just very vague with the office about why DD is away today
