Construx building sets from the '80's. Possibly on of the greatest building toys ever made. It's was DH's favorite toy as a child. He even used them for an AP science class way back in the day. We've scoured eBay and Craigslist for months and have a large array of sets and parts ready for DH to build something spectacular on Christmas Eve for DS to wake up to. We've shown DS photos and videos of the elaborate machines, dinosaurs, and even theme parks the people have created with them. It's hard to say who is more excited at this point, DH or DS. It's a gift for both of them.