I made my kids a sandbox with a folding lid. It folds up into two benches. Very practical!

Board dimensions:
Width 150 mm. Thickness 20 mm
Length:
for the box:
4 x 630 mm and 4 x 250 mm (shorter side cut at 45 deg)
for the lid:
3 x 1010 mm
2 x 1010 mm but 130 mm in thickness and two corners cut of at 45 deg making the shorter of two long edges 940 mm
2 x 640 mm shorter side and 94 mm
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Music in this video:
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Small Guitar by Bensound https://bensound.com