diff --git a/overviewer_core/settingsValidators.py b/overviewer_core/settingsValidators.py
index 08196cb..6476bb6 100644
--- a/overviewer_core/settingsValidators.py
+++ b/overviewer_core/settingsValidators.py
@@ -182,8 +182,20 @@ def validateStr(s):
     return str(s)
 
 def validateDimension(d):
-    if d in ["nether", "overworld", "end", "default"]:
-        return d
+    # these are provided as arguments to RegionSet.get_type()
+    pretty_names = {
+        "nether": "DIM-1",
+        "overworld": None,
+        "end": "DIM1",
+        "default": 0,
+    }
+    
+    try:
+        return pretty_names[d]
+    except KeyError:
+        if d.startswith("DIM"):
+            return d
+    
     raise ValidationException("%r is not a valid dimension" % d)
 
 def validateOutputDir(d):
diff --git a/overviewer_core/world.py b/overviewer_core/world.py
index b9548dd..e418d4b 100644
--- a/overviewer_core/world.py
+++ b/overviewer_core/world.py
@@ -121,8 +121,8 @@ class World(object):
             mcas = [x for x in files if x.endswith(".mca")]
             if mcas:
                 # construct a regionset object for this
-                rset = RegionSet(root)
-                if not rset.is_valid(): continue
+                rel = os.path.relpath(root, self.worlddir)
+                rset = RegionSet(root, rel)
                 if root == os.path.join(self.worlddir, "region"):
                     self.regionsets.insert(0, rset)
                 else:
@@ -151,15 +151,12 @@ class World(object):
     def get_regionset(self, index):
         if type(index) == int:
             return self.regionsets[index]
-        else: # assume a string constant
-            if index == "default":
-                return self.regionsets[0]
-            else:
-                candids = [x for x in self.regionsets if x.get_type() == index]
-                if len(candids) > 0:
-                    return candids[0]
-                else: 
-                    return None
+        else: # assume a get_type() value
+            candids = [x for x in self.regionsets if x.get_type() == index]
+            if len(candids) > 0:
+                return candids[0]
+            else: 
+                return None
 
 
     def get_level_dat_data(self):
@@ -236,17 +233,28 @@ class RegionSet(object):
 
     """
 
-    def __init__(self, regiondir):
+    def __init__(self, regiondir, rel):
         """Initialize a new RegionSet to access the region files in the given
         directory.
 
         regiondir is a path to a directory containing region files.
+        
+        rel is the relative path of this directory, with respect to the
+        world directory.
 
         cachesize, if specified, is the number of chunks to keep parsed and
         in-memory.
 
         """
         self.regiondir = os.path.normpath(regiondir)
+        self.rel = os.path.normpath(rel)
+        
+        # we want to get rid of /regions, if it exists
+        if self.rel.endswith(os.path.normpath("/region")):
+            self.type = self.rel[0:-len(os.path.normpath("/region"))]
+        if self.rel == "region":
+            # this is the main world
+            self.type = None
 
         logging.debug("Scanning regions")
         
@@ -265,34 +273,21 @@ class RegionSet(object):
 
     # Re-initialize upon unpickling
     def __getstate__(self):
-        return self.regiondir
-    __setstate__ = __init__
+        return (self.regiondir, self.rel)
+    def __setstate__(self, state):
+        return self.__init__(*state)
 
     def __repr__(self):
         return "<RegionSet regiondir=%r>" % self.regiondir
 
-    def is_valid(self):
-        """If this region set isn't one of the three known regions, then
-        return False"""
-        try:
-            self.get_type()
-            return True
-        except Exception:
-            return False
-
     def get_type(self):
-        """Attempts to return a string describing the dimension represented by
-        this regionset.  Either "nether", "end" or "overworld"
+        """Attempts to return a string describing the dimension
+        represented by this regionset.  Usually this is the relative
+        path of the regionset within the world, minus the suffix
+        /region, but for the main world it's None.
         """
         # path will be normalized in __init__
-        if self.regiondir.endswith(os.path.normpath("/DIM-1/region")):
-            return "nether"
-        elif self.regiondir.endswith(os.path.normpath("/DIM1/region")):
-            return "end"
-        elif self.regiondir.endswith(os.path.normpath("/region")):
-            return "overworld"
-        else:
-            raise Exception("Woah, what kind of dimension is this?! %r" % self.regiondir)
+        return self.type
 
     def _get_regionobj(self, regionfilename):
         # Check the cache first. If it's not there, create the