You can find a lot more details, including sample renders, in this article.
.ldr files are the same format and contain the model designs. The
.pov files are rendering instrcutions. All of the files are hand-editable.
ldd_tile.lxf file contains the Lego Digital Designer source for a single tile. It would cost around $25 to purchase, putting the whole game set at around $2000. Ouch! Any ideas for cheaper construction (beyond making the tiles more hollow/fragile) would be appreciated!
The LDD-generated instructions for building the tile are also included, although I had to tweak step 1 to including the parts list (appeasr to be a bug in the software) and some of the steps are not very clear at all (I'm looking at you, step 11).
7_complete files are for a 7-stud version of the tiles with less detail and no interlocking. The files include all of the tiles in the base game, along with the river expansion, as designed by FredWallace.