The party enters the crypt pictured in the map, and the door magically closes and seals behind them as they enter. The room is lit sufficiently with torches to allow normal sight.
On the map, there is a stone pillar at point A bearing the following inscription:
As time turns forward, so it goes
The path will open when we close
But should you fail the present task, it’s
Your fate to be in these caskets
The blood, of course, is the origin.
Then the life force drains. Begin.
Here’s how the riddle works. Each of the cross-hatched areas in the map represents a casket inhabited by a standard skeleton (Bestiary 1, CR 1/3) [SRD Link]. The caskets are open, and the skeletons are lying in them, inanimate. You may arm them if you prefer.
At point B, there is an elaborate fountain, maybe an animal’s head protruding from the wall, spilling water into a pool with a 5’x5’ drain grate in the bottom. The water drains out the bottom, but is replaced by the water from the fountain, so the pool is always at a constant depth of about 3’. The drain grate cannot be removed, and nothing will stem the flow of the water, which gives off a vaguely magical aura if examined.
To successfully pass this room, which is meant to lead into a deeper chamber, the party must figure out that the coffins must be closed in clockwise order (“As time turns forward, so it goes / The path will open when we close”), starting at the top left, marked with a red X on the map. Once that is done, the fountain at B stops, and all the water drains out through the grate at the bottom, leaving the pool empty. At that point, the grate can be removed (put a Strength check DC on it if you like, but a low one).
If at any point the party closes the wrong casket in the order, all of the skeletons in the open caskets rise up and attack, so the party will fight a maximum of 3 skeletons at one time. After the skeletons are reduced to 0 hp, they stagger back to their caskets and lie down again, and all four lids magically spring open. The cycle then starts again.
Make sure to track how many skeletons the party kills so you can award XP, and throw some XP in for the puzzle. To help the party along, there is blood spattered on the lid of the casket with the red X. Set a reasonable DC Perception check to notice it. This is indicated in the riddle (“The blood of course, is the origin.”) and the ultimate effect, the water (“life force”) drains away, opening the path forward.
You can put whatever you want in the caskets or in the crypt as a reward for the players. I would suggest a small gp reward.