Geology got interesting today, really interesting. Today I got to the business end of the cinder and pumice slopes of Pacaya volcano in Guatemala. Oozing gnarly orange lumps from weak spots like an old, metal toothpaste tube, the red-hot lava smashed and bounced down the slopes, spinning shrapnel firebombs off at frightening speed.

I perched on comfortably warm (but uncomfortably jagged) rocks that were formed only a few days ago, while nature's show just bubbled away nearby. Up the slope, a fellow trekker jabbed a walking stick into a crevice, pulling it out charred and glowing with embers. Downhill, a couple of English girls fresh out of university were melting marshmallows. How cool is that? Or do I mean hot? One clubbing-age woman yelped, "lava rocks!" Eventually, I suppose.

Without warning, a new crack appeared. Lumpy, grumpy lava bulged out. A crash, a crack and a massive slab liquefied and slid downhill. A wave of heat travelled the 100 metres between me and this most natural of barbecues. With it arrived a slightly worrying thought. Was I sitting on something similar?

With dusk, the bright orange of the lava intensified. In the valley below, the lights of Guatemala City and beyond that those of the original capital, Antigua, slowly awoke.

La Antigua Guatemala (the Old Guatemala) is a living tribute to colonial architecture, all precisely aligned cobbled streets with single-storey buildings of pastel shades. Hiding in secluded courtyards, travellers munch and slurp through menus and language students gorge themselves on verbs and vocab. Antigua is the Spanish-learning capital of Central America. It was devastated in 1773 by earthquake, so the city authorities upped sticks to ugly, sprawling Guatemala City. Many of Antigua's great churches, convents and monasteries are still in ruins.

Around this town, the volcano of Agua gently puffs, while Acatenango and Fuego look peacefully on, for now at least. In the coming days, exploring the Guatemalan highlands and Lake Atitlá*will provide some unforgettable memories with the volcanoes a permanent backdrop. But for now, Pacaya's playing her tune, singing her song. I'm very happy to be here to listen.

Footprint's 'Mexico & Central America Handbook 2009' is now available (£16.99)