If you're Grandboomers that live in the city and want to entertain your grandchildren, a science museum is a good choice.
Most major cities have some kind of science museum.
The beauty of them is that they're as interesting for the adults as they are for the children. There are loads of interactive exhibits and sights ranging from the prehistoric to space flight. It's time well spent. If you live in Washington, DC, your cup runneth over. You have multiple choices for science-type facilities that fill the bill.