From Lisbon:
Take  A5 (Cascais): exit  Carcavelos. Continue in the direction of Oeiras, going towards the Avenida Marginal, always going straight ahead at the roundabouts.
When you get to the Avenida Marginal, turn right, towards Cascais. At the next roundabout, turn right again and then immediately afterwards take the first left. Drive on, following the road as it curves to the right and you will soon see the Hotel Riviera in front of you, in the Praceta do Junqueiro.