We had not actually planned to go hiking to Boulder Cave when we were in Chinook Pass this past week, so we had not planned on flashlights. The only one we had along is the small one that is always in my husband's pack. The one in my pack was gone. I think I had lent it to one of the grandkids and not got it back.
A flashlight is not simply recommended in Boulder Cave. It is a requirement. In fact, make sure your batteries are strong, and it would be a good idea for each person in the party to have a flashlight.
Otherwise you will be using your camera flash for something like this:
It was fun. We hadn't been to Boulder Cave for at least fifteen years, though it was a frequent trip when we took the kids to nearby Camp Roganunda.Information about Boulder Cave can be found here.