icecave.des  - the ice cave portal vault

 portal.des   - portal vaults entrances

 sewer.des    - the sewer portal vault

not guaranteed. Furthermore, there is only one go at a portal vault - if
you leave, it's gone for good. Finally, you can apply special rules to a
portal vault, like enforcing maprot. Bazaars and labyrinths are typical
examples.

not guaranteed. Also, there is only one go at a portal vault - if you 
leave, it's gone for good. You can apply special rules to a portal vault,
like enforcing maprot.
Portal vaults can be particularly thematic, using specialised monster 
sets, fitting loot, coloured dungeon features etc. Avoid death traps; 
it is no fun to enter a vault, unable to leave and be killed outright.
Randomise in order to provide fun and reduce spoiler effects. For portal
vaults, it is desirable to have several different layouts (ideally each
of the maps has some randomisation on its own). Often, it is a good idea
to skew the map distribution: e.g. with four destination vaults, weights
like 40,30,20,10 might be more interesting than 25,25,25,25.
Portal vaults can be particulary thematic, using specialised monster 
sets, fitting loot, coloured dungeon features etc. Avoid death traps; it
is no fun to enter a vault, being unable to leave and be killed outright.
In order to provide fun and reduce spoiler effects, randomise. For portal
vaults, it is desirable to have several different layouts (ideally each 
of the maps has some randomisation on its own). Often, it is a good idea
to skew the map distribution: e.g. with four destination vaults, weights
like 40,30,20,10 might be more interesting than 25,25,25,25.