Nanoblocks. Nanoblocks are Japanese building toys, and the smallest block toy in the world. They are amazingly small micro-sized blocks, and they make Legos look like toddler toys. For any Lego enthusiast, these create a whole new level of construction challenge. The smaller the block, the greater the detail.
My children had tried (and succeeded) at several of the Nanoblock 'Mini Series' collection. As a result, I ordered them the Deluxe Himeji Castle set (pictured above). I loved this mostly because my husband and I traveled to Kyoto, Japan twelve years ago and spent a day visiting the 400-year-old hilltop castle complex. The 2200+ piece set took my children (mostly my son) some time to complete. He assembles a difficult Lego set in less than an hour. This took him about a week. There was a warning on the box stating it was not designed for children under 14, with a level of difficulty of 5, out of 5. Ha!
My children have also enjoyed recreating their 'Mini-Series' animals with Legos. Below you see my daughter's recreation of her penguin.