This activity may have been one I recently found on Pinterest, but it's also one I've known about for a long time. (That's just my justification for being too lazy to find the Pinterest source...) I made it more palatable by buying flavored marshmallows. They turned out to be a bit stickier than regular marshmallows, resulting in less-stable structures, but the kids had a blast. Honestly, I was done long before they were, but, like the Baking Soda Swamps, it kept them busy for quite a while and I didn't have to worry about the whining (fighting/screaming/crying/general insanity) that typically comes from their room.
I made the simple house for Henry because he was really overwhelmed at first and couldn't figure out what to do with his construction supplies.
He got into it, eventually.
I will definitely do this one with the kids again. Maybe next time we'll try regular marshmallows to see if those hold up a bit better.