Stretching for 96 square miles, the Grande Lago is Europe’s largest artificial lake, created to provide water for Portugal’s sun-baked Alentejo. And unlike the cities of the north and the beaches of the Algarve in the south, this part of Portugal — covering one-third of the country — is often overlooked by visitors.

As our little hired motorboat cruised along the still water, created when the Alqueva dam was completed in 2002, it was easy to believe that we had it all to ourselves. Staff at Amieira Marina, where we had our safety briefing and got the keys to the boat, have even reassured previous customers that it’s quiet enough to sail naked — if that’s what floats your boat.

My own clothes were staying firmly on, with plans to explore some of the fortified towns which dot the lakeside among groves of olive and cork trees, as well as to kayak to little islets along the way and star-gaze miles from any light pollution.

But the laid-back approach to life is one I was happy to embrace: our four-person boat had a top speed of 6mph, and even my nerves about getting behind the wheel (or getting lost) quickly dissolved.

Equipped with GPS, sonar and maps, there are also helpful marker buoys on the Alqueva lake, so you’re unlikely to stray far off course. And while my previous sailing experience was limited to a narrowboat and an inflatable flamingo, it’s all extremely straightforward, even for novices.

But even for more experienced crew, this lake is like few others. While its timeless feel could convince you that the flower-strewn landscape has existed under these cloudless skies for centuries, it’s less than a generation since this valley was controversially flooded, creating a vast reservoir that’s over 100m deep in places.

Hopping into our kayaks to explore the little islands dotted around, I had to keep reminding myself that these were actually the tops of hills. Look more closely and you’ll spy trees which seem to grow directly out of the lake, their roots lost on a bottom you can no longer see, while old roads weave casually down the hillside into the water, their final destination lost beneath the surface.

One village, Luz, was submerged completely, with a new re-creation built further up the hillside; the museum here has more background on the lake, as well as the history of the original Luz.

After the sun sets, the sheer number of stars against the inky black sky is breathtaking: the Alqueva Dark Sky Route stretches for around 1,150 square miles, a protected Dark Sky Reserve that includes the clear skies above the lake. Take binoculars or a telescope if you can, although you’ll see an impressive amount with the naked eye. There are also special activities and trails to follow for serious stargazers.

Another night we stopped at the smaller village of Estrela, with its whitewashed houses decorated with typical Portuguese tiles, one of nine villages around the lake where you can moor for free.

As well as our two double cabins on board our boat, the Campinho — bigger boats sleep up to 10 — there’s a small galley kitchen on board and a gas barbecue on the back if you prefer to self-cater as you sail.

One unmissable stop is Monsaraz: the fortified town was originally built by the Moors, when they controlled this area — later conquered and given to the Knights Templar in the 12th century, this peaceful area was once hotly contested borderland. Walking through the old gates onto the village’s steep twisting cobbled streets, you can climb up to the ramparts of the castle and gaze out across the landscape.

Those former occupants might well have stared out to a similar view of olive groves and vineyards: the Alentejo region is responsible for almost half of Portugal’s wine production and 90% of its olive oil.

But as I reminded myself once more, the shimmering ribbon of silvery blue watery stretching tantalisingly off into the distance wasn’t even two decades old. Even in the ancient heart of the country, there’s always something new to be found.

More secrets of the Alentejo

Discover the historic cities

Pretty medieval Evora is a Unesco World Heritage site, home to Portugal’s kings in the 16th century along with one of the biggest Jewish quarters in the country.

Evora’s synagogues no longer remain but you can stroll the shady streets past buildings which once housed the Jewish community, not far from the main Praca Giraldo —Rua do Tinhoso, Rua dos Mercadores and Rua da Moeda in particular.

The city was also an important stop on the trading route in Roman times. The Roman temple of Diana is one of the best preserved on the Iberian peninsula, while a huge aqueduct still stands outside the city walls.

A more uniquely macabre attraction is the town’s bone chapel: the Capela dos Ossos is constructed using human remains of around 5,000 people, excavated as the city grew in the 16th century.

Further south, Beja has its own Jewish heritage as well as Roman history. The town is also home to a Visigothic museum, housed partly in a 6th century church that’s one of Portugal’s oldest standing buildings, and makes a great base for exploring some of the area’s vineyards too, such as Herdade da Malhadinha Nova.

Head to the beach

The Alentejo coast isn’t nearly as well-known as the beaches of the Algarve or the sea around Cascais and Estoril, but that means you won’t need to share the sand with anywhere near as many people.

You’re more likely to find fishing villages than big resorts, but it’s perfect for those who love surfing as well as discovering the area’s wildlife. On the Troia peninsula, you can spot dolphins, visit the Carrasqueira stilt village and discover more Roman ruins.

The navigator Vasco da Gama was born at Sines, where a world music festival is held in early summer: today it’s significantly more industrial but worth a short visit if you’re exploring the beaches nearby. 

To the north, you’ll find bays with lagoons for canoeing and windsurfing, while to the south, the beaches including Vale Figueiros are good for families. Porto Covo, Vila Nova de Milfontes and Almograve are among the most popular, especially with surfers.

Walk the Rota Vicentina

This walking and cycling route stretches across the Alentejo and the Algarve, with almost 250 miles of trails along the coast, past fields of wildflowers, nesting storks and even the chance to spy otters.

As well as two main sections of the Rota Vicentina, the Historical Way and the Fisherman’s Way, there are eight circular routes if you don’t fancy tackling the entire thing, including walks from Almograve and Troviscais, which you could combine with the beaches.

Stay in a Pousada

Some of the most unusual and unforgettable accommodation in Portugal, the converted historic buildings known as pousadas, include unique places to stay, some with royal links. 

And the Alentejo is home to several; choose between pousadas in Evora and Beja, the Pousada Alvito housed in a 15th century castle, plus the Pousada Convento de Vila Vicosa near Estremoz, a former 16th century convent built to house the daughters of the nobility.

Next to the Ducal Palace, this hotel has a swimming pool and summer dining in the cloistered garden, along with 39 converted rooms, including family rooms. Driving distance from Evora, as well as Lake Alqueva, a seven-night stay costs from £752 per person B&B, including return flights and car hire. Book with Sunvil.

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