From Uyuni we went onto Potosi, with the bumpiest bus journey so far, although good scenery and lots of llamas. Potosi is the highest city in the world at 4100m and a fascinating place - certainly my new favourite - full of narrow winding streets, colourful old buildings, red-tiled roofs, beautiful churches, and women in traditional dress all over the place. Potosi is famous for it's silver mountain ('Cerro Rico') which once made the city one of the richest in the world - The Spanish discovered it in 1545 and locals have been mining it ever since, pretty much without change. During the colonial period 8 million black slaves and Indians died either down the mines (they'd be sent in for 6 months at a time without coming out once) or in the processing plants, where they seperated minerals using mercury just with their hands.

Our tour down into the mines was the most fantastic, interesting and eye-opening out-of-my-world experience I've ever had (hence fifth coolest moment of expedition - they just keep coming). And great fun too, largely due to our hilarous guide called Pedro. We started off by getting kitted up in wellies, overalls, helmets and head torches, before heading off to the miner's market, where we brought some dynamite (Pedro: 'smell this, smell this. It's not cocaine. It can make you fly, but in pieces'), 96% alcohol (ooh, that burnt), and gifts for the miners. After that we went and had a look round a processing plant and got our faces painted with silver, before heading into the mines themselves.

There are eight layers to the Potosi mines and 12,000 people still working in them, most of whom speak Quechua and not Spanish. We managed to get as far as the third layer and that was more than enough for most of us. In the first level we could walk upright, just about (with little carts rattling along rails in a complete Indiana Jones stylee), but further down we had to crawl along on our hands and knees to get through the hot, claustrophobic, dusty tiny tunnels full of horrible chemicals and little oxygen. Any miners we encountered (some of them pulling along trucks full of 1 or 2 tonnes of minerals, between only 2 or 4 of them), we gave gifts of alcohol, and watched them sprinkle it over the ground first to Pachamama (mother Earth) before drinking any. We saw teenagers younger than us sweating away inside the mountain (the youngest working in the mines is only eight, and the average life expectancy is about 40 to 50 years), and passed others with great wads of coca leaves inside their cheeks, which they chew continuously to give them energy and so they don't have to eat. We also saw one of the many statues of the devil that they have inside the mines, who rules the underworld and hence who they offer up alcohol and coca leaves and cigarettes to, to ensure their luck continues.

After coming up out of the mines we went and prepared our own dynamite and blew up a teddy bear, and it was the funniest sight watching Mel, Nick and Karen frantically running down the hill with their lit dynamite so they could get rid of it before anything happened.

The following day in Potosi most of us went biking to an amazing volcanic lake, which was the exact temperature of a plesantly warm bath, and had the most fantastic barbequed llama afterwards.

And then we came to La Paz, which is where I'm frantically trying to update this from before packing for trek No. 2 tomorrow. La Paz seems like a really cool city. Unfortunately I haven't seen much of it yet, having spent most of my time wandering along only one street, which is where all the instrument shops are. We have visited the witches market though, with little stalls full of potions, talismans and dried llama foetuses.

Last night was Karen's 30th and Aussie Sarah's 23rd, so we all got rather drunk, the four guys dressed up as girls, and went out to the restaurant/bar Mongo's. Among other things I demonstrated to Karen how to do a cartwheel in the bar (she had 30 challengs to complete during the night, of which one was cartwheeling), fell over on the floor when Nick flicked me on the arm, taught everyone the Cat in the Microwave dance (Rachel, that one was for you), and spent most of the evening insulting our leader Paul (42 going on 18 half the time, but a wicked person). When I wasn't insulting him we had great deadly serious conversations about complete shit. Paul spent the meal in Mel's tankini top with a pink hat, pink scarf and fingerless gloves to accesorize it ('Paul, you look like a complete tit'), and also had Karen's finger-puppet tocan on his hand too, which kept drinking from my wine glass. It was a good night.