2024 NOTE: Check whether Benagil is accessible before visiting. In late 2023 it was briefly closed due to overcrowding and a kayaker getting injured by a motorboat. There is a public consultation due to finish June 2024. https://participa.pt/pt/consulta/gt-grutas-de-benagil-instrucao-de-navegacao (link in Portuguese). Until that finishes, the area may be legally closed to visitors when the waves are high.
Benagil Cave is where even non-kayakers go kayaking. It’s one of the symbols of the Algarve – a sandy beach inside a large cave, with two entrances and a skylight. It can’t be accessed from land, and motorboats can enter but aren’t allowed to let off passengers, so to experience it properly you need to swim or paddle in. Some of the big motorboats do a “hybrid tour” where the passengers are disgorged into double sit-on-tops for the last hundred metres. It’s also a couple of hundred metres to swim or paddle from Benagil Beach – turn left and follow the crowds.
There are rental companies for sit-on-top kayaks and SUPs at Benagil Beach itself, although the hourly rate will be steep compared to a longer term rental from Decathlon. They don’t rent them out when the surf is greater than a metre high. The departure beach is small and south-facing so if southerly winds are strong (usually a winter phenomenon) then the surf gets up and you may be out of luck unless you are an accomplished surfer, in which case you could rent a surfboard instead and hand-paddle that in, Check the wave forecast ahead of time here. https://www.surfline.com/surf-report/praia-do-carvoeiro
The area is very busy in summer and you will probably come across many inexperienced kayakers, swimmers and bodyboarders falling over in the surf and getting in each other’s way. In high summer a lifeguard on a board maintains order, keeping the motorboats, kayakers and swimmers all apart. If it is busy and there is no lifeguard, sometimes the motorboat drivers can get intimidatingly close – stay near to the left wall as you enter the cave and make sure you are seen.
If you want the place to yourself go either very early or late in the day, as many of the operators clock off before 6pm.
There are other (less popular but quieter), paddles on the surrounding coast, see Portimão to Albufeira coast. Further west is the other big kayaking attraction in the area, Lagos and Ponta da Piedade.