The Arrábida itself lies further south, beyond Palmela, but the estuary is worth a paragraph of its own because it shapes everything about this part of Portugal.
The Tagus widens here into a vast lagoon-like expanse, among the largest wetland areas in western Europe, protected as a nature reserve. Mudflats, saltmarsh and reedbeds attract tens of thousands of waterbirds in winter, and flamingos are a regular sight, sometimes pink lines drawn along the water's edge. Spoonbills, avocets and herons feed in the shallows. The surrounding fields hold rice paddies, and the area has a strong tradition of horse and cattle breeding, with the cattle herders known as campinos wearing a distinctive red waistcoat and green stocking cap.
The roads around the estuary are flat and fairly dull to ride but pleasant in a slow way, running between poplar rows, drainage ditches and the odd old warehouse. Samora Correia and Alhandra, the closest towns, offer fuel and food. Alhandra is a small riverside town with an old waterfront that has seen better days but still smells of tide and diesel in a way I like. In the evening, small restaurants serve grilled fish, clams and eel stew, the sort of cooking that comes from the river rather than the sea.
If you head south to the real Arrábida, you reach one of the most beautiful stretches of the Portuguese coast. The Serra da Arrábida rises steeply above the sea, with white limestone cliffs covered in Mediterranean scrub, a monastery on the hillside, and a coastal road to Setúbal that offers sea views at nearly every bend. It is relatively short but wonderfully twisty, and best ridden on weekdays outside the high summer, as the beach traffic can slow everything down.
Wind from the Atlantic is common, and mornings may bring mist over the water. In autumn and spring the light is soft and the birds are at their best.