If you are traveling in Portugal I definitely suggest to visit the Nazare lighthouse.
If you have never heard about this place please check numerous video in Youtube of extremely large waves crashing against rocky lighthouse in Nazare.
How to get there?
The most convenient option is rent a car. The road from Lisbon would take 1.5 hours by car, from Porto - 2 hours. Be careful, mostly roads in Portugal are toll road. The free parking near the lighthouse (10 min by walk) is available. The entrance fee to lighthouse platform - 1 EUR.
Otherwise there is bus connection from Lisbon Sete Rios Station. The ticket costs 13 EUR (2018).
Taxi option is near 90 EUR.
So, why the waves are usually so huge in Nazare?
The most essential part of Nazare’s oceanic miracle is the Nazare Canyon. It locates in one kilometer from the shore and reaches a depth of around 5 km!! (That two times bigger than the El Capitan mountain).
Usually, the waves slow down and shrink when approach the coast because the rising seabed level which is pushing back the swell. But when the bottom occasionally falls (like in case of Nazare Canyon), the waves get more and more energy as the water rushes to fill the sudden free space. Thereby, the biggest waves form at Nazare, are the result of two swells — one coming from the canyon and one from the shallower continental shelf — converging and gaining due the interference.
Substantially, the waves are so big because they are two waves stacked atop one another.
Here are some of my photo dated January 2019. I was not lucky, because the weather was for 100% calm; thus waves were quite small. But still it was impressive. Could you imagine what is happening there in windy or stormy weather? 
