I built one (from plywood) a couple of years ago for my then-7-year-old daughter for Christmas. She never appreciated it fully but I've enjoyed it a little. One of these days I'll build a more serious one. I was reading the other day about the Pythagorean scale of perfect intervals which was used before the compromise of even tempered scales came in. Lap dulcimer seems the ideal instrument to experiment with the Pythagorean scale.