Buffalo Bayou, the original corridor of settlement, runs along the north side of downtown. Sam Houston Park recalls this first community; above it rises a web of freeways. The commercial district runs east 14 blocks to the George R. Brown Convention Center. The Theater District extends north and east of Sam Houston Park. Several 19C buildings have been preserved at Old Market Square; the original Allen's Landing is three blocks beyond. More than 50 blocks (about 6mi) of downtown are interconnected by the growing Houston Underground, a tunnel system that shelters the working population from summer humidity and winter rain, not to mention year-round street traffic.