Physics teacher and explorer Simon Chapman seeks hidden cities of gold in Bolivia.

Towards the end of term I found it increasingly difficult to stay focused on getting everything at school ready for September. I kept remembering that I might soon be face to face with a jaguar.

The story of how I'm spending my summer began a little more than 500 years ago when the Inca Yupanqui sent his army to the swampy grasslands of Southern Amazonia to conquer the troublesome Moxos people who refused to succumb to the might of his great Andean empire. The army failed in its mission. The "savages" the Incas had expected to meet turned out to be highly organised - civilised, even - walling themselves up behind great earth ramparts topped with palisades of sharpened spikes and only venturing out to slaughter the visitors from the mountains once the Incas' supplies were low and their numbers had been reduced by disease.

The ructions caused by such a defeat were still reverberating around the Inca empire when the Spanish arrived a couple of years later and finished the job.

But who's heard of the Moxos? Theirs is one of the "Cities of Gold" myths that became absorbed into all the other El Dorado stories. There's certainly no great civilisation there now (like most Amazonian tribes, the Moxos succumbed to influenza and smallpox). But there may still be lost cities to discover, and this summer I'm off to look for them.

This is a 10th-anniversary return trip to Bolivia for me. A decade ago, I quit my job teaching physics in a high school in Manchester and took a folding canoe to go looking for a man-sized ape that was said to inhabit the Andean forests of northern Bolivia. I didn't find it, but I later wrote The Monster of the Madidi about the journey (TES Friday magazine, April 6, 2001). Now I'm going back with my companion from my first trip, Julian Singleton, and the same team of guides (Irgen and Leo Janco), but this time we'll be heading away from the mountains. The terrain will be flat, and probably marshy. How do you find a lost city in these parts? Look for a hill; it'll be man-made.

The last written account of exploring the pampa was by Leo Parcus, a German soldier who arrived after the end of the First World War seeking adventure.

He survived a jaguar attack, saw his guide bitten in half by a crocodile and was captured by cannibals; if you believe it all, he certainly got what he was looking for.

Barring hostile animals, my expedition has much the same flavour. We are about to canoe the rivers and lakes of the region in a lightweight Pakcanoe that we'll roll up and carry on overland stretches, and we hope to hire horses from cowboys we meet along the way - this is real gaucho country.

Unlike Leo Parcus, we have serious technology on our side; I'll be using a global positioning system (GPS)to find our location every night. To organise the trip, I communicated with my guides via email and mobile phone. And as on my two previous expeditions (to Siberia in 2003 and Brazil in 2001), I'll be sending messages - diary entries and map co-ordinates - to schoolchildren at summer schools in Knowsley near Liverpool. As well as monitoring our progress, they are linking up with a reserve in Brazil for their project on jaguar conservation.

Simon Chapman is head of physics at Morecambe high school and author of the Explorers Wanted! series for children (Egmont) and The Monster of the Madidi (Aurum Press). Follow his progress for the next six weeks in The TES and keep up with the Knowsley project at www.spiritofthejaguar.org.uk