Tulum - my how you've changed!

No Internet access here, but my BlackBerry is working so I've been sitting on the beach outside our room (about 30 meters from the sea) exchanging emails with my agent and the desk editor at Scholastic re some final touches for the book.

Tulum has changed a lot since I was here with my husband and fellow biochemistry student, Becs, almost 20 years ago. Back then we hired a taxi for $80 US dollars and the taxi guy drove us down from Cancun, hung around the makeshift car park while we traipsed around the ruins, carefree as you like. On the tiny but gorgeous beach by the ruins we met some people from Didsbury, Manchester of all places (where I grew up). The sea was rough that day. The whole area was experiencing the beginning of what would become a tropical storm. We drove back along the coastal road with the windows down - no aircon and stopped en route for a swim at the blue, blue lagoon of Xel-Ha. (pronounced shell-ha)

Around 3 weeks later the storm became Hurricane Gilbert and devastated Tulum.

These days Tulum is a BIG tourist trap, Xel-Ha too. Big car park, coach loads arriving all day long, massive arts and crafts shops and restaurants. Official tourist guides take you round and give you a terrific spiel, all the latest findings. No more free wandering around the ruins, no more clambering over the pyramids.

Ernie, our Mayan guide explained how all 52 structures in Tulum played their part in a ceremonial centre which also functioned as an astronomical and weather calculator. He showed us the place where at around 5am on 13 November the light from the rising sun passes though a small window in one temple and lights up the door in the surrounding wall - to the west. This would be the signal to harvest the last of the crops before winter. Another portal would trap light to signal the time to sow. And by an amazing feat of engineering,the Temple of the Wind God uses a pole and a temple window to raise the alarm of an approaching hurricane, whistling like a flute when the wind speeds start to get dangerous.

Tulum is a city with natural protection from invaders - mangrove swamps to the west, the Caribbean to the east and offshore, a long reef which prevented Spanish from landing anywhere close. So why did they need to build a 6ft high wall all the way around the ceremonial centre? It's the only example of such a wall in a Mayan city.

Ernie gave us the latest explanation - and it's ingenious. "Tulum's biggest danger was always the hurricane" he said. "Where do you put 2000 people in a place like this, to protect them from the hurricane?" The buildings held at most 600 people - and they were in danger of having their palm rooftops ripped away. The answer was this: the wall. It was long enough for all 2000 people to line up behind the wall as a shelter.

Ernie is a bona fide Mayan - comes from a tiny place deep in the interior of the Yucatan peninsula. "If you want to see the real Mayan people," he chuckled, "get a guide to take you in a 4x4, and tell him you want to go where the tourists don't go. He'll take you where you won't hear a word of Spanish - only Maya."

Well maybe next time. Our kids are way too whingey for that right now. The heat and crowds of Tulum got to them. Chances are that Becan and Calakmul - in the Campeche jungle to the south - is going to be too much.

All the way down from Playa del Carmen, the highway cuts through the jungle. I peered into the trees. Poor Josh Garcia - in "Invisible City" he spends hours lost in there. Me - I wouldn't dare to step 20 meters into that place.

Tomorrow, Chetumal, the state capital of Quintana Roo and the place where Josh's Mayan adventure begins...