Sure.
Basically it is a “hidden” map, that can be only unlocked by finding and interacting with certain runes on three maps from “Return to Ubersreik” DLC. I suggest just checking YT for it, it is quite long process.
Once done however, a “Dwarven Lodestone” situated just next to Bridge of Shadows in the Keep will unlock a hidden, fourth map: Fortunes of War.
In this gamemode, Olesya breaks a spell around a hidden treasure. The map is basically a big market square with a statue in the middle and Olesya places lightning runes around it to break the spell.
In practice it means, that you’re facing waves of enemies in particular order. The spawns are fixed and once defeated/after certain time next wave is triggered. The fight consist out of eight phases/waves, with each phase having a sub-wave of enemies. Later phases have progressively more sub-waves, with the wave 8 having 9 sub-waves of enemies. If you die, you will respawn only at the end of the phase. That means, that if you die at the beginning of the last wave No 8, then you will be dead till either the rest of the team wins or dies trying.
The beginning spawns are fine, but around phase 5 things start to get tricky. Last phase is crazy, you will have a total of four bosses, all possible specials + multiple patrols spawning right after each other. Forget about defense in the corner, you will need to bring out your A-Game.
Luckily, spawns are fixed. You know what is coming and where it is coming from, so you can prepare for that. Still, I consider this map the ultimate vanilla VT2 challenge, as you will be forced to kite alone a boss (or bosses), patrols, random mobs and zerkers while trying to spot & eliminate different specials coming at you in very, very uncomortable combinations. Even high-level weaves are easier, as they can be cheesed.
Once all enemies are defeated, you unlock a treasure in the middle that will henceforth decorate your Taal’s Horn Keep and also get a sweet frame.