Make your own marble run!! Awesome toy to engage both kids and adults. Max value as there's no upper age limit (I sat there for an hour having fun building it myself). If you have Duplo or Lego blocks at home that are getting stale, get some Hubelino sets to spice them up. Made in Germany and 100% compatible with Duplo/Lego, these pieces offer limitless play and brings building-block fun to the next level.
They even have more advanced elements like a catapult launcher, funnels, etc. Note though, you do need quite a fair bit of lego/duplo blocks if you want to build more extensive systems. Look on Amazon and compare pricing, I found some there to be cheaper including shipping than if bought locally from some specialty toy stores in SG.