The Bog Mummies

This fully prepped dungeon is best used with high level adventurers who are unafraid to solve conflicts through social means and unafraid to flee. The conceit of the dungeon is that it is a tomb of a cult to Akun-Ray. The low level adherants guard two rings on the first level, as well as the entrance. The high level adherents guard the final floor, which is both the prison and the throne room of Akun Ray, who is far weaker than his servants and thus unable to leave "for his own good". 

There are multiple entrances to this ruined tomb, hidden in a valley in a boggy, loamy environment. The most obvious is a staircase down to the front doors, which are locked and guarded by two flameskulls, which animate and attack as described in the image below.

The second most obvious is an ancient druid circle atop a nearby hill:

At the top of a treeless hill four hundred feet East of the main entrance there is a near perfectly circular ring, about 2 feet thick, 2 feet tall, and 20 feet in diameter. The center of the circle has what looks like a large rune burned into the grass.

A DC 11 Nature check will cause you to notice there are no stones anywhere within 1 mile.

DC 14 Arcana check to recognize that the rune is an ancient Giant symbol for transportation. Knowledge of Giant or Druidic means you automatically succeed this. 

Digging into, setting something large onto, or rolling a DC 11 Investigation check on the ring will reveal that 6 inches below the surface are several massive wooden logs, steambent and shaped into a circle.

Continued digging (at least 4 feet), or a DC 14 History check will reveal that this is a Woodhenge, and that there are several posts supporting this ring of logs. If this is discovered through digging, ancient Giant inscriptions can be revealed on the inside of the ring that explain plainly the function of this structure. 

Bringing a stone into the center of the circle will cause you to teleport to the central circle in the dungeon.

The third and final option to enter the dungeon is to dig. One out of six rooms (roll randomly) on the first floor are partially caved in, revealing depressions on the surface where one can dig a few feet to find a peripheral entrance to the dungeon.