DIY Sand and Rock Box by FSPDT. Gdjk -> made this with toilet rolls (aka tunnels) and moon sand instead of play sand. My son loved playing with it. The moon sand cleans up nicely indoors but play sand will be easier to play with when using the small cars.
Free Plans - Build a DIY Activity Table - Addicted 2 DIY Build a 4 in 1 Activity Table for kids. This makes a great addition to any playroom and keeps the kids entertained for hours between trains, coloring and more.