Orgrimmar Fortresses are buildings appearing in Orgrimmar during To Tame a Land and in Tidefury Cove during Old Hatreds.
For the first one, Thrall and Rexxar's stash can be found there. It corresponds to Grommash Hold in the Valley of Wisdom.
The first Fortres in Orgrimmar.
The second Orgrimmar Fortress in Tidefury Cove.