The team working on Total War: WARHAMMER II have put out a new development post about one of the free features being added in the next update and it sounds really fun.
Recently, The Hunter & The Beast expansion was announced that seems quite feature-filled but it's also coming alongside a big free update too. Part of this update is the inclusion of "hyper defensible" Forts for the free Mortal Empires campaign map that you get if you own both Total War: WARHAMMER games.
You've battled across the map in various locations but there's currently nothing quite like this.
I'm definitely interested in a battle through a Fort! Linux gamers have a bit of a wait though, as the free update which includes the Forts and The Hunter & The Beast expansion will release for Linux "shortly" after the Windows release on September 11th.
Read some background development info on Forts on the Total War blog post. They go over the process of designing them, with each taking quite some time to make. They also said they will be showing them actually in action some time later this week!