Easy: There is an almost overwhelming amount of magical energy filling the entire room.
Moderate: The energy seems to be emanating from the idol itself.
Additionally, to any PC with experience in the Underdark this energy seems a bit familiar. To any gnome PC, the energy is familiar and even welcoming.
If the PCs send someone in first (with some people staying outside), there is a kind of spacial warping effect - they move normally but can't cover the distance between the door and the statue. There are no apparent exits from this room. If the characters decide to give up and leave, you could have them turn around and go back the way they came... only to have the same room appear before them in the other direction. This should suffice to should the PCs that they all must enter the room. As soon as the last one steps inside...
The second you step inside, you feel a slight bump at your back. When you turn around, you see nothing but a smooth wall. A moment later, you blink and find yourselves standing in a semicircle around the illuminated idol.
Easy: This appears to be a gnome deity.
Moderate (or Easy for a gnome PC): This is Calladuran Smoothhands, god of the svirfneblin.
Difficult (or Moderate for a gnome PC): Calladuran Smoothhands is a neutral deity, the god of the darkness beneath the earth, magic, protection, and... trickery. (Mwahahahaha!)
"Six and one and one and six.
Every sixty seconds, one will mix.
One to life and six to death,
All before one draws one breath.
Six steps to take, one choice to make:
An oath to swear, a vow to break,
A sin confess, a wrong redress,
Six souls into my service press,
One precious memory, allowed to fade.
Then the choice shall be made!
Six to die and one to live,
No other clues shall I give."
As the words fade out again, seven doors appear on the far side of the wall.
If you don't want to repeat yourself about a million times, print out copies of the poem for all your PCs. The PCs must pick a door to go through. If they pick a door at random, any PCs standing in front of the door are blasted back by magical energy and take 3d6 damage and the room begins to spin (see below). After that, if they persist at picking at random, you can have the voice speak again:
"Cheater cheater!" The doors will no longer budge.
Once the PCs understand the rules, start the timer! One minute in game-time doesn't equal one minute in real-time - I set the timer for one minute, but gave them some leave-way on either side. After running this, I'd say about three minutes on the timer would be perfect. If three minutes seems too long the first time, shorten it by 30 seconds each time. And each time the timer runs out...
An other-worldly giggle fills your ears, and the room starts to spin. Faster and faster and faster until it's everything you can do to resist being thrown against the walls!
Athletics or Acrobatics Check (everyone must roll)
First time - Easy: You manage to keep your feet.
Second time - Moderate: The room was moving faster than before, but you were able to prevent yourself from being thrown against the wall.
Third time - Difficult: The room is moving faster than ever. Only by throwing yourself to the ground do you avoid injury.
Failure: You are thrown violently against the wall. First time - 1d6 damage. Second time - 2d6 damage. Third time - 3d6 damage.
I scaled this up for my 16th level PCs, but if you don't want to do too much damage (and why wouldn't you?), you can stay at 1d6. If you are scaling up, a good way of creating tension would be to place 1d6 in front of you when the timer starts. When the PCs don't figure out the puzzle and complete the tasks in the first three minutes, have them all roll their checks. Once you've resolved the damage, place 2d6 in front of you. Don't forget to smile!
I added a little red herring to the mix - I had orcs passing by this way, and they had made marks in code around the doors. One of my PCs has the Comprehend Language ritual... but it takes 10 minutes. Heh. If the PCs persist and somehow manage to crack the code, it says things like "Fidgug sez dis un" and "Burzob sez dis un." Seven different orc names are used (here's an orc name generator), each saying "dis un" - only the orcs know who is telling the truth. Heh heh.
The solution is pure role-playing. One PC must swear an oath, one must break a vow, one must confess a sin, one must redress a wrong, and one must sacrifice a precious memory. Additionally, all the PCs must swear to serve Calladuran Smoothhands (in some capacity). If you have fewer than six PCs, you can change the line to "Your souls into my service press." Not as cryptic or fitting with the poem's theme, but hey - needs must. After a PC completes a step, a light shines on them and one door disappears. Once the PCs complete the tasks, only one door remains - and soon the door itself falls away to reveal a clear passage out of the room.
As you walk out of the room, the voice sounds in your head, "That was fun. Good luck!" You feel a surge of magical energy flow through you. You believe that you will, indeed, have good luck.
All the PCs get a +2 attack bonus to their next use of an Encounter or Daily power. That should take some sting out of the damage they've taken (especially if they fall over the whole "orc code" thing). A side note - you can substitute just about any neutral/unaligned trickster god in this scenario. Have fun with it.