Six days in Nicaragua: two colonial cities that could not stand each other, and a lava lake in between

Go to the cathedral within an hour of it opening, because the part you want is the roof and it is in full sun. Construction started in 1747 and the building was inaugurated in 1780; the towers and the façade went on between 1810 and 1820. It is the largest cathedral in Central America and a UNESCO site, and Rubén Darío, the poet who reinvented verse in Spanish, is buried inside it under a mourning lion.

Buy the separate roof ticket, take your shoes off and go up. The roof is a field of whitewashed domes you walk between barefoot, with the city on one side and a chain of volcanoes running north from Momotombo on the other. Down at ground level, Central Park in front is where León sits in the evening, and six of the eight streets meeting the square are now pedestrian.

Cross the square afterwards to the Museum of the Revolution, which is not a museum in any conventional sense. The displays are thin and labelled in Spanish only. The guides are former Sandinista fighters who were in the battles being described, they take you round themselves, and at some point one of them will point out a photograph of himself at nineteen with a rifle.

The Ortiz-Gurdián is the surprise of the country. Four colonial houses on one block were knocked together to hold it, so you move through courtyard after courtyard with the collection on the walls: strong twentieth-century Nicaraguan and Latin American painting, colonial religious work, pre-Columbian pieces, and a European room with a Picasso, a Chagall and a Miró in it. Even if the art does nothing for you, the buildings and the shade will.

Five minutes away is the house Rubén Darío grew up in, now a small museum of his manuscripts, furniture and belongings. Darío invented modernismo, which is to say he is the point at which poetry in Spanish stopped imitating Spain, and Nicaragua treats him roughly the way England treats Shakespeare. Azul, the 1888 collection that made his name, is sold at the door.

Finish at the Recolección, three blocks north of the square: a church consecrated in 1788 with a Mexican Baroque front in an aggressive yellow, covered in twisted columns and medallions. It is the best façade in a city with a great deal of competition and it looks best in the last hour of light.

Take the morning out to León Viejo, about forty minutes east on the shore of Lake Xolotlán. The city stood here for its first eighty-odd years, until earthquakes and the volcano above it persuaded everyone to move west in 1610. What survives is the ground plan of an early colonial town, excavated and left low: the Calle Real running up to the plaza, the footings of the cathedral and the churches, the houses of the men who ran the place. Momotombo stands directly behind it and does most of the work.

The interest is in how small it is. This was the administrative centre of a Spanish province and the whole thing would fit inside a village. The remains of the conquistador Pedrarias Dávila were found here, along with those of the rival he had beheaded in the plaza, and there is a small museum on the indigenous people of the lake shore. There is almost no shade.

Come back for lunch, sit out the heat, and go west in the late afternoon. Sutiava was a separate indigenous town swallowed by León, and its church is among the oldest and biggest here, with a plain wooden interior instead of gilt. On the low hill above it stands El Fortín de Acosasco, a Somoza-era fort used to watch the city and to hold political prisoners. It is a ruin, and the reason to climb it is the view of León with the whole volcano chain behind it.

You have to change buses in Managua, so use the city rather than the terminal. Just after midnight on 23 December 1972 an earthquake destroyed the centre of the capital and killed thousands of people. Much of the rubble was cleared and the middle of Managua was simply never rebuilt, which is why the old cathedral still stands as a roofless shell in an open space, its walls cracked and its interior closed off, with grass around it.

Walk from there up to Loma de Tiscapa, the hill above the crater lagoon. The presidential palace and the headquarters of the National Guard stood on this spot until the same earthquake took them, and political prisoners were held and tortured in a building nearby. What is on the hilltop now is a black steel silhouette of Sandino, twice human height, and a view over the lagoon, the lake and a capital that has no discernible centre.

Then go on to Granada, forty minutes southeast, and give the evening to walking. The cathedral at the head of the central street is mustard yellow with a white trim, floodlit after dark, and the streets running away from it are lined with single-storey houses in strong colours with barred windows and interior courtyards you catch glimpses of. Sit in a courtyard bar and do nothing.

Masaya is the reason to be in Granada rather than only passing through. It is about half an hour away, and it is one of very few volcanoes anywhere with a road that takes you to the crater rim: you drive up, park facing the exit as the rangers require, and walk to a railing above the Santiago crater. Below, through the sulphur, there is molten rock moving. The Spanish called this the mouth of hell and planted a cross on the rim to seal it, which is still up there.

Go for the last entry of the day. In daylight the crater is a grey pit full of gas; after dark the lava lake glows orange and the smoke above it lights up from underneath, and the difference is total. Time inside is limited and rangers move groups on, so this is a short, extraordinary visit rather than an afternoon.

Before that, spend the middle of the day in Masaya town. El Coyotepe is a nineteenth-century hilltop fortress that the Somozas used as a political prison, with dungeons underneath that guides will take you into with a torch and a panoramic view over the town, the lagoon and the volcano from the walls. Down in the town, the old market is a crenellated stone building from the end of the nineteenth century that looks like a castle and sells handicrafts from all over the country, with a folklore museum inside it.

Have a slow last breakfast in Granada. Café de las Sonrisas, a few streets off the square, is a café and hammock workshop staffed almost entirely by deaf, blind and mute Nicaraguans, with the sign language alphabet painted round the walls so customers can order. The hammocks are woven on site and are the best thing you can carry home from this country.

Then go back through Managua, and if the flight is late enough, stop at Acahualinca on the way. In the mud of an old lakeshore, four metres below the modern ground level, are the footprints of about ten people walking towards the water some six thousand years ago, preserved under volcanic ash and now sheltered in a small museum. Children's prints run alongside adults'. Nobody knows whether they were fleeing an eruption or simply going to the lake.

The museum sits in a rough part of the city, so arrive by car and keep the driver with you. The airport is half an hour east of there, which makes this a genuinely easy last stop rather than a detour.