Syntax: enter (held portal)
enter <object> (in-room portals)
To use a hand-held portal, hold it and type 'enter'. If you are trying to
use an in-room portal, type 'enter <object>'. In either case, you will be
taken to the destination of the object held or in room. Portals have a
fixed destination. Some portals (such as the psionicist's nexus) have an
accompanying portal back; sometimes, though, this is not the case.
If you have the portal wish, typing 'enter' will take you to the
destination of the object held in the <Portal> equipment slot.