door_to

door_to is a property defined by the standard library which allows for >ENTER OBJECT (where object leads to another location). Obviously, it is used by the door class defined in objlib.h, but it can be used for lots of other things.

room castle "Castle"
{
     long_desc
           "Inside, the castle is exactly what you expected - tacky and featureless
            with ant eggs near the top and gravel at the bottom. To anyone else, the
            colours sprayed randomly on the wall would just be colours sprayed randomly
            on the wall. To a daring inter-dimensional espionage operative like yourself,
            however, they are obviously used to focus communications across the dimensions.
            The only exit is out, back to the goldfish bowl. Your attention is drawn
            to a glass box resting in the middle of the room here, this looks like Panchax's
            work.
            \nA smooth warp, a jagged warp and a small warp are also clearly the boss's
            work."
}

scenery smoothwarp "smooth warp"
{
     in castle
     article "the"
     adjective "smooth"
     noun "warp"
     long_desc
          "The smooth warp looks the trendiest of all the warps. It must lead somewhere
           pretty cool."
     door_to clearing
}

Which gives us:

>enter smooth warp
Inter-dimensional travel hurts. A lot. Especially when you haven’t done it for a while. You buck and roll through the journey, feeling very nauseous, then, with a small popping noise, take over a body with the aid of a customised host-parasite interface. Your host has arms and legs. Looks like trouble!

Clearing
It’s stopped raining here at the moment, but the clouds overhead show that it could start again any minute. If they decide to burst, the tree stump in the centre of the clearing would probably fill up with water. Paths go south, southeast and east. In all other directions the undergrowth is too tangled to make any progress. Micky Blowtorch, your ex-colleague, now a crazed warp junkie, is lounging around the stump, looking suitably bemused.
>

More castles

Here is another example since Johnny wants to see some moats and drawbridges, oh my!

room bythemoat "By the Moat"
{
    long_desc
         "You are in front of a moat. Yadda yadda."
}

scenery moat "moat"
{
      article "the"
      noun "moat"
      door_to
            "You don't feel like a swim right now."
      in bythemoat
}

object drawbridge "drawbridge"
{
      article "the"
      noun "drawbridge" "bridge"
      when_open
            "The drawbridge is down."
      when_closed
            "The drawbridge is up."
      door_to {
              if self is open
                   return insidecastle
              else
                   "The drawbridge is up."
              }
      is openable
      in bythemoat
}