A tomb older than the towers.

What Ca na Costa is.

Ca na Costa is a burial monument made of large upright stones set in a rough circle, with a chamber in the middle that was once covered by a mound of earth and small stones. It stands on flat ground near the lagoon rather than on a hilltop, which is part of why it stayed unnoticed for so long. The slabs are local limestone, grey and weathered, standing upright in thin soil. Nothing here is reconstructed; the stones are the stones that were set.

The date comes from the burials and from the shape of the monument. Archaeologists place its construction at about 4,000 years ago, which makes it the oldest known monument on the Pitiusas: older than the Phoenician sites on Ibiza, older than the churches and the coastal towers. The chamber held more than one burial. Excavation in the twentieth century found those burials and a small number of objects placed with the dead. The people who built it farmed, fished and kept animals on an island with no harbour walls and no salt pans.

Four thousand years of weather, and the stones are still standing where they were set.

Getting there from Es Pujols.

Ca na Costa sits on the lane that links Es Pujols with Sant Ferran, on the inland side of Es Pujols and close to the edge of Estany Pudent. From the village it is a walk of a few minutes, flat the whole way, first on pavement and then on a track. From Sant Ferran it is a similar distance in the other direction. The site is signposted and the stones are visible from the road. The whole approach is flat, so it suits anyone who finds steps difficult.

Bicycles are the easiest way to combine the tomb with the rest of the island, since the lane is level and the distances are short. Island buses link Es Pujols, Sant Ferran and Sant Francesc Xavier, with more services in summer than in winter; check the current timetable with the island bus operator before relying on one. Anyone driving should leave the car in Es Pujols or Sant Ferran and walk, because the verges are narrow.

• On footA few minutes of flat walking from the centre of Es Pujols, or a similar distance from Sant Ferran.
• By bikeThe lane is level and quiet, and the green routes pass close to this part of the island.
• By busIsland buses link Es Pujols, Sant Ferran and Sant Francesc; check the current timetable first.
• By carLeave the vehicle in Es Pujols or Sant Ferran, since the lane has no proper parking.

When to go.

The tomb stands on open ground, so a visit is not tied to a timetable, but the light matters. Early morning and the last hour or two before sunset are best: low sun rakes across the upright slabs and brings out the grain of the limestone, while at midday in summer the flat ground around the chamber holds the heat. Spring and autumn are the most comfortable seasons for standing still. Winter light is low all day and the lane is quiet.

In July and August, come before the beach fills or after the day has cooled. Outside the main season the lane is quiet, the lagoon behind the tomb often holds water and birds, and the monument takes on a different character altogether. Much of Formentera's tourist business closes roughly from November to April, but the stones do not, and Es Pujols and Sant Ferran stay inhabited all year. Fewer buses run in winter, which matters if you are relying on them.

What you are looking at.

A single information panel explains the structure, and it repays a slow read before you walk around. The circle of upright slabs formed the walls of a chamber; the gaps between them were closed with dry stone, and a low mound covered the whole thing. What remains today is the skeleton of the monument, stripped by excavation and by centuries of weather, but the plan is still legible if you walk a full circle. The stones are not dressed or carved, and their effect comes from size and arrangement.

Slabs of this size had to be dragged, levered and raised by people working with rope, wood and muscle, and the effort says something about what the tomb meant to them. It was used over time rather than once, and it probably worked as a marker in the landscape as much as a grave: a low, solid circle near the water, visible from the lagoon and from the track that crossed the island. No other monument of this kind is known on Formentera.

Visiting without leaving a mark.

The monument is unprotected by walls or glass, which is both a privilege and a responsibility. The stones are old and brittle, the soil around them is thin, and the plants that hold it together grow slowly. Stay on the path, do not climb on the slabs or sit on them, and do not move or take stones, shells or fragments of any kind. Everything on the surface is part of the record.

Erosion is the real threat. Feet on the same line widen it year by year, so walk at the edge of the visible track rather than single file through the same rut. Keep voices low, leave drones in the bag, and carry out anything you carried in. Groups should spread out and keep to the outside of the circle. The tomb has come through four thousand years of weather; it should not be worn away by a decade of visitors.

• Stay on the pathThe soil and the plants around the stones are thin and slow to recover.
• Keep off the slabsThe upright stones are brittle and the chamber is not built to carry weight.
• Take nothingFragments of pottery and small stones are part of the archaeological record.
• Leave the droneQuiet is part of the visit for everyone else on the lane.

What to bring.

This is a short stop on flat ground, so the kit is minimal: water, a hat and shoes you can walk a kilometre in. In summer the lane and the ground around the tomb have almost no shade, and the heat coming off the limestone is stronger than the sea breeze suggests. A light layer helps in spring and autumn, when the wind crosses the island from the north. There is nowhere to shelter if the weather turns.

Bring a camera for the texture of the stone rather than for a wide view, and something to sit on if you plan to stay with the monument for a while. Binoculars are worth the weight, because Estany Pudent lies close and the shallow lagoon draws birds through the year. Anything you bring should go back with you, since bins on the lane are few and often full.

• WaterThe nearest shops and fountains are in Es Pujols or Sant Ferran, a walk away.
• Sun coverHat, sunglasses and sunscreen; shade near the monument is scarce to none.
• BinocularsThe shallow water of Estany Pudent draws birds in most months of the year.
• Stout shoesClosed shoes cope better than sandals with the stony track and rough ground.

What is nearby.

Es Pujols is the nearest base, a small resort with a beach on the sheltered side of the island and the usual seasonal services, much of which closes roughly from November to April. Sant Ferran, a short walk inland, has a village square and stays alive all year. The lagoon of Estany Pudent lies alongside the lane and forms part of Ses Salines Natural Park, with shallow water and birdlife. Bicycles can be left at the edge of the track without blocking it.

The green routes for walking and cycling run through this part of Formentera, which makes the tomb a natural stop on a half-day rather than a destination on its own. Sant Francesc Xavier, the capital, is a short ride west, with its fortified church. Ses Illetes and the salt flats lie further north, and the two lighthouses, at La Mola and Cap de Barbaria, are longer rides east and south.

Practical notes for the visit.

The ground is level and the walk short, which makes the tomb one of the easier prehistoric sites to reach with children or with a pushchair, though the last stretch is unsurfaced. There is no shade, no toilet and no visitor centre: this is a monument in a field rather than a museum. The nearest facilities, and the nearest cafes and shops, are in Es Pujols and Sant Ferran.

Allow a quarter of an hour at the stones and rather more if you are walking both ways. Because the site is open, plans rarely fail here, which makes it a useful stop on a day when wind or cloud has changed your mind about the beach. The visit is short, so combine it with the lagoon and the village rather than making a special journey. For questions about access, signposting or work on the lane, the Consell de Formentera is the body to ask.