We start this one coming from Setúbal, but other entrance routes are available.
If you do the main avenue near the city port, you will end up in a road that enters Serra da Arrábida natural park (a protected nature area). Just keep going forward and you will be doing the lower road in the loop. The tarmac is a little inconsistent and bumpy and with the beach crowds in the summer and some police presence, a moderate pace is advised. This section of the road is occasionally one way only (your current way).
You are now going by the lower part of the cement factory (yes, there is a cement factory in a natural park!) and some beaches. Proceed straight forward in the Portinho da Arrábida intersection (a great beach spot) and you will arrive at another intersection at the end of the road, turn right here and you can start the upper section of the loop.
The tarmac up here is much better and the view even more so, also, less traffic. There are some straight sections, but some very interesting corners.
Be careful when approaching the quarry (yes, there is also a quarry!), the road is full of dust.
After the quarry, you will come to the end of the road, turn right, go past the cement factory and back to your starting point. From here you can redo the loop (right) or go for Setúbal (left).
Since this is a natural park, please avoid littering, excessive speeds or very loud pipes.
If you do the loop early in the morning you can avoid the beach crowds, police, cyclists, boyscouts, etc.
400 bends. Some in 2nd gear, scrapping, others 4th, scrapping, to No traffic