Split Timeline Dungeon

The Frost Keep of Altruzix was built high in the peaks of the winterspine mountains to isolate it from the rest of the continent, due to the intense magics being used and developed that could affect the surrounding areas in unnatural ways.

The keep has been abandoned by its creators for hundreds of years, until an invading army attempted to invade to claim the massive magical power sources that are rumored to be housed inside, the battle against the magical guardians that protect the keep from invaders was so destructive that one of the power sources was ruptured, and it froze time for the entire keep and the surrounding area.

Rooms of the keep
There are several rooms within the keep, and each room has two frozen timelines linked to two separate magical rods. When one rod is used, frozen creatures/environment within that rod's timeline will move through time at varying speeds and react to their environment as appropriate. If a timeline is ever advanced beyond the final 'resolution' of the battle, the scene resets everything (including the players) to the state the room/world was in before the players entered.

The rods will pulse with magic in varying ways to let the party know when they are destabilizing the timelines, sometimes this can lead to time resuming for a short time, or time just resetting completely.

=the front gates= This area appears as a battlefield with rows of archers lining to fire upon a single line of defending construct guardians defending the entrance, dead soldiers at the construct's feet already. The keep has several ballistae constructs firing from above as well. Timeline 1 - the archers firing their arrows at the shield guardians. Timeline 2 - the Shield guardians advancing toward the archers, and the ballistae bolts firing toward the archer lines as the front gate portcullis closes. The trick is to advance the archer's timeline to allow for several shots against the constructs, then advance the construct's timeline just enough to allow them to take damage from the arrows and be destroyed, but if not enough damage is done before advancing the construct's timeline, a second set of constructs will fall from the keep's defensive wall. If the constructs timeline is advanced too far, they will overrun the archers and pursue the party.

If both timelines are advanced simultaneously, the battle will play out and the invaders will be killed.

=The main hall= A room divided into two sections, the entrance side with some soldiers advancing into the room to support their ranks on the far side of the room, between them lies a bridge. There are wizards that have already cast several destructive spells towards the bridge, but their spells are frozen in time. Timeline 1 - a battle between construct and invaders rages on the far side of the room, reinforcements are crossing a bridge to the far side. Timeline 2 - wizards are casting spells toward the reinforcements on the bridge, their magic frozen mid-arc towards their targets. The trick is to either let the constructs win the fight, and pursue the party after the invaders are dead then advance the timeline to destroy them on the bridge, or to cross the bridge and allow the invaders and bridge be destroyed and wizards will turn their attention to the battle and will wipe out both sides, including the party if they aren't careful. Once the constructs are dead, a door will open for more constructs to reinforce the battle, allowing the party passage further inside.

Within the dungeon when the magical accident occurred, there was a battle being waged across the entire dungeon in order to halt the flow of time by a wizard deep within, who was trying to buy time to finish their spell to defend themselves and their guardians. Instead, the entire dungeon was frozen, including the wizard, and no one has been able to unlock its secrets.

Each room has one or two timeline elements present, and all are frozen still in time until someone moves the timeline with magic. Each room will reveal a scene or battle, or some sort of normally urgent event that they can resume the timeline for with a magic item.

For example, archers and their volley of arrows exists on one timeline, while the defenders raising their sheilds exist on another timeline. If one timeline is triggered beofre the other it may offer an advantage to one of the other, with consequences or rewards.

All frozen items/people are indestructible and immovable by any means other than a wish spell, magical items are excluded from this effect. No sentient creatures caught in this magic time warp are able to see, hear or otherwise sense  anything ocurring in present time, only the timelines that were affected by the intial magical experiment.