Oh sorry on a certain part okay, i thought it was just a map,
You can maybe use this
mapname,x,y,0 script ontouch -1,3,3,{
OnTouch:
warp "mapname",x,y;
close;
}
the -1,3,3 specifics the cell range, so if you can specifiy the x and y cell range of that part of the map and put an npc there, you can make them warp back to town