What goes up must come down. At the Maya archaeological site of Chichen Itza in Mexico’s Yucatan peninsula, that can be a problem.

I had visited the site once as a college student many years ago, experiencing the wonders of a civilization the flourished from 600-1250 before internal strife caused it to collapse. (For more details on this fascinating culture, see my visit to Tulum in the January 2005 issue of this column.

On my recent trip to Chichen Itza, the most popular Maya tourist site and one of the area’s finest, I remembered the challenge of Kukulkan’s Pyramid, also called El Castillo. One of the largest Maya pyramids in the Yucatan, the structure has great archaeological interest. Each of its four sides has 91 steps, which added to the top platform equal 365, the days of the year — one of the many physical reminders of the Maya fascination with numbers.

More interesting, however, is the reason the steps were built. Dedicated to the feathered serpent god Kukulkan, who is thought by some to be the Maya version of the Aztec deity Quetzacoatl (for more on this, see weber.ucsd.edu/~anthclub/quetzalcoatl/que.htm), the pyramid features stone snake heads flanking the base of each staircase. Impressive in themselves, these heads help the pyramid celebrate the snake-deity in a fantastic, distinctly Mayan way: harnessing stone to work magic with light.

To experience this magic, one must visit on the spring or fall equinox, which I did in my long-ago spring break visit. One the 21st or 22nd of March and September, between noon and 5 p.m., the pyramid casts a snake-shaped shadow that seems to slither along the ground. Another shadow seems to illuminate a bright, snakelike strip moving down the north-facing steps. It is an amazing feat of ingenuity to position this enormous building to manipulate shadows with such precision.

This visit, I missed seeing that aspect of the pyramid, and I was told that it now has become so popular that visitors during the equinox can expect extremely crowded conditions. What I could re-experience in August, however, was the excitement of climbing to the breathtaking top.

Formerly, this privilege was reserved for the high priest elite, who would walk the length of each wide step before ascending to the next one in a serpentine motion. Today, people of all ages eagerly scramble in the heat (bring something to wipe your face with, you’ll need it!) to experience the impressive views of the ruins and the peninsula. In every direction stretches jungle, interrupted only by the spots where people long ago carved out places to live, worship and play — and where today’s archaeologists have uncovered these reminders.

And then comes the hard part — heading down. The stairs are quite narrow — a normal shoe stretches beyond the edge — and the effect is startlingly unsettling. Recently, a rope has been added, running down the middle of one stairway, but since it is not banister height, the help is largely psychological. I went down sideways, keeping a reassuring hand on the step just above me.

Once you reach the bottom, there’s more. The structure is actually a pyramid within a pyramid. The Mayas had two calendars, and every 52 years they coincide. To mark the event — or, some believe, to celebrate their survival of Halley’s comet, which swept over Mexico in 857 — the current pyramid was constructed over the smaller, inner building.

From my college days, I remember an odiferous, claustrophobic trip into the inner structure, so I didn’t try it this time around. The more courageous visitor will be rewarded with the sight of a red-painted jaguar, messenger of the gods, studded with 73 spots of jade. He crouches there just as he was constructed more than 1,000 years ago.

Another extraordinary thing about this tourist destination is the Great Ball Court, the largest such court to be discovered in Mesoamerica. This was the site of an extraordinary game some believe to be life-and-death: A 5-point rubber ball was to be propelled through sideways hoops on either side. (Here the sun obsession reappears: during the solstice, the sun shines through the hoops.) And the ball, shaped like the sun and therefore sacred, couldn’t be touched with hands, feet or head. Players wore pads on elbows, hips and wrists in a game that often lasted for hours. While there is some indication that the winner was beheaded, it is also argued that the sacrifice was symbolic only. The game is re-enacted for tourists today at nearby Xcaret (presumably without the deadly reward!).

A third attraction that makes this Maya ruin unique is the Sacred Cenote which some believe was also the site of human sacrifice. The entire Yucatan peninsula is flat and waterless, without rivers or streams. Underneath the surface, however, underground water flows, made accessible to humans when the limestone surface collapsed and created wells, or cenotes (say-NO-tays). This impressive expanse of green water, sheltered in a limestone basin and flanked with the ruin of a sweatbath, was home to the rain god Chac, to whom maidens and athletes may have been offered. Only about half a dozen skeletons have been found in its waters, however, even though the Maya culture flourished at Chichen Itza for more than 1,000 years, leading some scholars to dispute the notion of regular sacrifices.

If you visit this extremely popular attraction, be prepared for crowds. It is best to book a tour through your resort, or through an organization such as www.cancun-discounts.com, www.cancunfuntours.com or www.cancuntravelcenter.com. Rumor has it that the stairs up Kukulkan’s Pyramid may be closed to tourists in 2006, so adventurous travelers should make the trip soon!

Happy traveling!

Photos: Climbing to the top of Kukulkan’s Pyramid affords spectacular views, but going down those narrow stairs can be anxiety-producing. The hoops in the ball court are cunningly situated to catch the sun during the equinox. The Sacred Cenote, a green, glistening well, was said by some to have been used for human sacrifice.