I made this map, using Campaign Cartographer 3 for my Basic Fantasy campaign. The PCs had to enter the bullywug lair to rescue captured villagers. The lair consistes of sunken pit dwellings contected by underground tunnels. The entrance to the lair was a hole in the ground above the square chamber at the bottom of the map.
If you can use this map, then you have my permission to do so for your personal use. Download it from here.