The King's tower has, as of patch 1.24, a total of 450 floors. You will be rewarded for defeating the enemies of each floor, and thus permitted to ascend to the next. You can find King's Tower in Dark Forest, it is available after beating stage 2-12. Rewards include both types of Soulstones (Elite Soulstones for every 10th floor and Rare Soulstones for the rest of the floors), Gold, Hero's Essence and Diamonds. Rewards increase with every conquered floor to became substantial amounts later in the game.
The King’s Tower, once the beacon of mankind was an illustrious gleaming tower from whence the old king ruled over his kingdom. It wasn’t until the old king was betrayed by his younger brother, Prince Edwin, that the tower began its descent into darkness. The tower in which so many cruel deeds took place now stands enshrouded by darkness as if it were a monument to evil.
Towers of Esperia
Unlocked after completing stage 15-1 in the Campaign.
There are currently only 4 other Towers themed after the respective factions, hopefully with Towers for Hypogeans, and Celestials being added later in the game. You may only use Heroes from the faction that the tower is themed after. You can only complete 10 floors per day and the different towers are rotated out on a daily basis.
There are campaign quests you can complete by finishing floors in all Faction Towers. A detailed list of rewards can be found here - Towers of Esperia Rewards.
Tower of Light - Lightbearer Heroes
Opens every: Monday/Friday/Sunday
This shining edifice was erected millennia ago by King Anion in memory of his grandfather, King Luther, the first king of men and the first bearer of the light. Many champions of men have attempted to reach the zenith of this inspiring monument, seeking to pay homage to the old king, yet have failed in surmounting the challenges that face them along the way. The path to the old king’s sky tomb is treacherous and full of hidden dangers. Only the most resilient and resourceful are capable of summiting this cloud-capped trial of stone to pay their respects to King Luther.
The Brutal Citadel - Mauler Heroes
Opens every: Tuesday/Friday/Sunday
Nestled between mountainous peaks, this daunting citadel is carved directly into the rock. Its unassailable facade brandishes hard angles like weapons, seeming to challenge all who view it. Behind its walls, torch-lit arenas ring with the sounds of clashing weapons and brash taunts. A regular stream of fresh mauler warriors descends on the place, all eager to prove to themselves and the assembled clans that they are worthy of their Mauler moniker.
The World Tree - Wilder Heroes
Opens every: Wednesday/Saturday/Sunday
This gargantuan tree draws Wilders of all stripes to its impossibly wide trunk. Inside, it is crisscrossed with meandering corridors, not carved but integrated into its growth pattern through ancient magics. The interior surfaces are covered with ropes of branch and vine that support the wondrous tree like a woody musculature. Those with an affinity for the forest find themselves inexplicably drawn to this behemoth, as to ascend to the canopy is to find oneself communing with the heart of the natural world itself.
The Forsaken Necropolis - Graveborn Heroes
Opens every: Thursday/Saturday/Sunday
Once a place of final rest for the dearly departed, the necropolis now houses a new ominous tenant. Long gone are the days where the dead could rest and the living honor their memory. The evil that walks these halls has warped the natural order into a twisted perversion of itself. Dread energies enshroud this accursed place, where the once peaceful silence has been supplanted by the skittering sounds of bones against cold stone.
Don't expect to be able to use Faction Bonuses to your advantage. While you are restricted to using 1 type of Faction for each tower, your enemies will not have that restriction.
Because of this, it's recommended that you should approach each stage with a higher team Attack Rating than that of each stage.
If you are having difficulty completing a stage you can try re-arranging your hero formation or checking out team compositions that others have used. Sometimes even just swapping your two frontline heroes can make all the difference. You can also use the help of some mercenary heroes.