Antonio's fishing boat bobs on the glassy surface of a huge crater lake, dwarfed by a panorama of dramatic volcanic peaks. Beneath us the water plunges to a depth of 240m, perhaps more. "Now we are at the deepest part. They call it the place with no end," shrugs Antonio. "This is a good place to swim."
Like many of the fishermen on lake Ilopango, Antonio swims for a living, using the traditional and dangerous method of freediving to catch fish from the shallower parts of the lake. I, however, am a bit concerned about what strange creatures may lurk beneath, and certainly don't want to try to catch anything. I stare at the sparkling water, only to hear squeals of delight from behind me. A group of local boys are launching themselves from the branches of a tree almost 10m above the water. My competitive streak kicks in – if a 12-year-old kid can swim here, so can I.
An ungainly tree-scramble later, and I'm free-falling into the bottomless warm water to the sound of my own screams and loud hilarity from the shore. Like so many experiences I have in El Salvador, it's completely unexpected, a hell of a lot of fun, and features volcanoes in some form. We are, after all, smack bang on the Pacific ring of fire.
There 21 other volcanoes here, the smallest and most densely populated country in Central America. This particular firecracker, Ilopango, to the east of the capital San Salvador, exploded in 260AD in an eruption so powerful that the ash reached Iceland. It left behind the largest lake in the country, stretching 72 sq km, with dramatic cliffs and lava rocks. It is now known for its fantastic scuba diving, but as I don't dive I've opted for an hour's tour on a local fishing boat. As we sail, Antonio recounts stories from the civil war of 1980-92 when soldiers used the now bullet-scarred rocky islands for target practice and would call the fishermen out afterwards to collect the fish killed by the explosions. He tells me you can still find bullets at the bottom of the lake.
Back on the shore, I share a beer with the locals as the sun sets over the water. We sit at a plastic table at one of a string of stalls, eating fresh shellfish served with lime. This friendly, unscrubbed section of the northern shore is where Salvadorians come to escape the city. Families are still swimming as the light fades and two grinning children run up to me, the only tourist here, to show off their pet – a tiny green bird with its wings clipped.
Part of the attraction of this country is that it's so small you can drive from east to west in just seven hours, north to south in four, hopping from beach to pretty colonial towns or heritage sites in a day. It's convenient to stay either in the city or by the beach, and make day trips. The inter-American highway cuts through an astonishingly green landscape, saturated in season with the red foliage of los flamboyan – flame trees.
The following morning I make the short drive southwest out of San Salvador to another legacy of El Salvador's eruptive past.
The Unesco world heritage site at Joya de Cerén is known as the Pompeii of the new world – a whole Mayan village that was buried under the ash of nearby volcano Loma Caldera for 14,000 years until it was discovered by accident by a bulldozer in 1976. Yet while you can visit hundreds of Mayan sites that offer a window on to the world of the ruling elite, Cerén uniquely provides an insight into the lives of ordinary farming people. The museum guide proudly tells me that even Mexicans, famed for their spectacular Mayan temples, will make the trip here. Incredibly, no human remains were found – it seems the villagers had enough warning to escape – but in their hurry to evacuate they left almost everything behind. Their houses, last meals, crops and tools were all preserved in the ash, and can now be examined – free from the crowds and pushy sellers that swamp some Mayan temples.
On my way back to the city I make a detour along the La Libertad coast road, Carretera del Litoral, which links a string of surfing beaches. Some have a cluster of hotels and restaurants, at others there's nothing but a camp ground and seafood restaurant run by fishermen. This coast featured in the iconic 70s surf movie Big Wednesday, and perhaps the best-known break is Punta Roca. It's just 25 minutes out of the city, so school kids skip class to ride bus 102 (tickets cost about $1) to the waves. During the civil war it was the one place where opposing soldiers would sit in the same restaurant to enjoy some seafood at the beach.
Some 7km further east is El Sunzal, the fastest-growing surf spot in the country. Pink bougainvillea decorates a steep cobbled road to the beach, which is home to the only left-hand break on this coast. A surfer "village" of accommodation has built up over the last decade or so, ranging from $3-a-night camping pitches to $30 hostels or poolside balconies for $150 a night at El Roca Sunzal, a friendly surfer hotel. Two bars on the beach ensure a good party at weekends.
Back in San Salvador, I meet up with local guide Eric for a visit to perhaps the country's most iconic volcano – that of San Salvador itself. Accessed at El Boquerón national park, its highest peak, El Picacho, is wreathed in smoke-like clouds and dominates the skyline.
San Salvador is called "la ciudad de las dos caras de la moneda" – the city of two sides of the coin – because of the split between wealthy districts and poor areas downtown where people make a living hawking whatever they can sell – DVDs, food, hammocks. But for all San Salvadorians, the sleeping giant holds great significance, lying so close that the city's western edges encroach on its slopes. As Eric and I climbed towards its gaping crater – 1,600m in diameter and 500m deep – he told me a story about the city's eponymous volcano.
As teenagers during the civil war, Eric and his friends were curious to explore this symbol of the city. During wartime, travel was dangerous and maps were forbidden in case they fell into the hands of insurgents. But youthful curiosity got the better of them and they decided to climb the volcano – a decision that almost cost them their lives when they narrowly escaped being kidnapped by guerillas. Eric still has the bullet scar on his right arm from the shots that pierced their car as they sped away.
Although the war is long over, for many Salvadorians, being able to see the sights on their own doorstep is a relative novelty. Maps still hold magic for some, and they are proud and eager to share their country with visitors. But for the time being, at least, you are more likely to enjoy El Salvador with the locals rather than other tourists. It's their open-armed welcome and generosity that leaves me vowing to return to this small, often overlooked corner of Central America.
Iberia (iberia.com) flies to San Salvador from Heathrow via Madrid (inc connecting flights from San Jose-Costa Rica, Guatemala or Miami), from £730 rtn. Hotel La Posada del Angel, San Salvador (hotellaposadadelangel.com). El Roca Sunzal (rocasunzal.com/). Guide with papagayoadventures.com. For further information on El Salvador and other destinations in Central America, go to visitcentroamerica.com.
Journey Latin America (020 8747 8315, journeylatinamerica.co.uk) has just launched packages for El Salvador. A 10-day trip costs from £1,063pp excl flights.