A boat trip around coast of Lagos, to Ponta da Piedade is a must if you are visiting this part of the Algarve. The unique rock formations and grottos are a spectacular sight.   Boat trips leave from Av. Dos Descobrimentos (along the river), in Lagos and cost €10 per person for around 45 minutes.  You can also get trips from Ponta da Piedade, but this requires a steep climb down (and up!) the cliff steps, and you could have a long queue for boats at this point.  To see the most on your trip you will need to go at low tide, mid morning worked well as is was also not too hot.