Praia da Duquesa, also known as "Redondo" or "House reef" is the best access spot in Cascais. This place is protected by the law from any potentially invasive activity (including diving), so a special authorization from the Maritime Authorities is required to dive in the area, which is sometimes granted to local diving centers of Cascais. The fact that this diving spot is part of the port area - and thus also granted a special protection - has also favoured the protection of the whole ecosystem, creating excellent conditions for many species of organisms to thrive in the area.
This spot extends until about 250m to the South of "Casa do Duque de Palmela" house. Being an area which is well sheltered from the prevailing North and Northwest winds, it usually offers good conditions for diving, with good visibility. It is undoubtedly a place with ideal characteristics for try dives and refresh dives, as well as for night dives. It should nonetheless be noted that although this area is very protected by land and sea (due to the entire structure of the Cascais Marina), when the winds blow from the South it is totally exposed. In times of great rainfall (even with favorable winds and sea), the very sedimented waters coming from the Tagus river as well as those that come from the streams all over the coast can reach the place and soil the water at a moment's notice, not allowing for great visibility.
The excellent accessibility conditions of this spot also allows for great diving initiatives such as the "Dive for All" inclusive dive, geared at physically disabled divers. Also, during the bathing season, when the "Beach for Everyone" program is in operation, there is a facility at this place with resources (amphibious tricycles, walkers) and personnel that seek to facilitate access to sea to people with some mobility limitations.