'Hidden' Sand Pit

southernsun

We are planning to re-design the garden of our new home as the previous owners have covered the whole garden in pathing slabs and decking. We have a plan of what we are going to do and part of that involves keeping a section of decking approx 4.5m wide by 5m long (its currently 4.5m wide by 16m long)). I had an idea to build a sand pit into/under the decking and wondered if anyone had any tips/ideas on how to do this.

My thinking is to have the sandpit (wood frame or a big plastic mould) put into the ground under the decking then a wooden lid put on top of this to keep water out and then screw the decking boards to the lid. Then to use the sand pit we can lift the decking/lid off and when its not in use and the lid is on it looks like normal decking and therefore takes up no extra space in the garden.

Thinking size wise it would be 5 ft x 5ft max so taking up about a sixth of the overall decking area.

Can anyone see any problems there might be with this. Would wood rot under the decking and would a wooden lid with decking on cause any problems with rain drainage/water getting into the sand pit. In my head this is a fun/space saving idea but not sure how practical it is.

Any advice/tips will be gratefully recieved!