Lagos (pronounced [ˈlaɣuʃ] ⓘ; Proto-Celtic: *Lacobriga) is a city and municipality at the mouth of Bensafrim River and along the Atlantic Ocean, in the Barlavento region of the Algarve, in southern Portugal.

Lagos is one of the most visited cities in the Algarve and Portugal, due to its variety of tourist-friendly beaches, rock formations (Ponta da Piedade), bars, restaurants and hotels, renowned for its vibrant summer nightlife and parties.

The Moors fortified the town with Lagos Castle and established important trade links to Northern Africa from their bases in the Iberian peninsula.

Lagos was also the home port for Gil Eanes who was the first to sail beyond Cape Bojador in 1434, after a failed attempt in 1433 that put him out of favour with the, then considered the end of the world.

When, by 1443, Lançarote (then fiscal officer of the crown) had sailed as far as Arguim and brought back 275 Africans, the Portuguese had sufficient slaves to relieve the perpetual handicap of agricultural labour.

[12] From the first slave markets in Lagos (the Mercado de Escravos, which opened in 1444), many Africans were dispersed throughout Europe, bringing a considerable income to the Portuguese monarchy and merchant classes, as well as cheap labour force.

[14] Following the death of Prince Henry, and the expansion into the Atlantic and New World, the port of Lagos continued to receive shipments of goods and slaves, but its role began to decrease.

By its geographical position (east-northeast to west-southwest orientation) and lithological diversity, the Algarve stands out as a unique stratigraphic and morpho-tectonic region.

[18] A peripheral Carboniferous unit of the Variscan orogeny, it constitutes the Mesozoic and Cenozoic sedimentary layers, deposited onto two totally distinct superimposed basins.

[18] Between the Middle-Upper Triassic to Hettangian, sediments evolved from continental (fluvial red sandstone) to shallow marine over the entire region, which included instances of evaporates, tholeiite fissural magmas, lava flows, volcanic ash and pyroclasts.

[18][19][20] A period of calm during the intra-Miocene (of approximately 2.4 Ma) led to generalized exposure and development of karst, that influences the present day coastline.

[18][20] The conspicuous horizontal bending of this profile in the cliffs of Lagos, much like the remainder of the Lagos-Portimão formation, is formed by alternating bands of siliciclastic and calcareous lithologies.

[19] The littoral and cliff sands are dominated by various bivalve organisms, bryozoans, larger benthic foraminifers and Coralline algae with minor additions of echinoids and balanids implying a shallow-water depositional system of a warm-temperate climatic regime.

[19] The locality of Cerro das Mós, from where a large crocodilian (Tomistoma schlegelii) tooth was collected long ago,[21] has also produced some Odontoceti teeth.

To the north of Lagos is the road to Silves, the first capital of the Algarve, Monchique (spa town/mountain), Milfontes, a coastal town and port/harbour of the city of Sines, that winds through the scenic protected landscape of the Southwest Natural Park (Costa Sudoeste Alentejana e Vicentina).

Lagos is also a wine-producing region and is famous for its moscatel wine, and also for a strong alcoholic spirit, the aguardente de medronho, made of berries of strawberry tree.