This itinerary links two of Lisbon's closest and most visited destinations in a linear loop without returning to the city between them. The Linha de Cascais runs west from Cais do Sodré to Cascais; the Scotturb bus 403 connects Cascais to Sintra (30--40 minutes, check current schedules at scotturb.pt); the Linha de Sintra returns to Rossio in Lisbon.
Book accommodation in Cascais and Sintra before race week; both towns fill for weekend stays even in December.
Lisbon Cais do Sodré → (40 min, Linha de Cascais) → Cascais (1 night)
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(Scotturb 403 bus, ~30 min)
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Sintra (2 nights)
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(40 min, Linha de Sintra) → Lisbon Rossio
December conditions: Cascais (12--16°C, Atlantic wind) and Sintra (8--12°C, misty, cooler due to the Serra altitude) have different microclimates separated by 30 kilometres. Pack layers. December is significantly quieter than summer at both destinations.
Night One: Cascais
The Linha de Cascais runs along the Tagus estuary and then the Atlantic coast from Cais do Sodré, arriving at Cascais in 40 minutes. Trains every 20 minutes.
Cascais became the summer residence of the Portuguese royal family in 1870 and the combination of working fishing port and aristocratic resort remains visible in the architecture of the historic centre. The core is flat, sitting on a low coastal shelf.
The seafront promenade runs west along the bay from the fishing harbour toward Estoril - paved, flat, and exposed to the Atlantic, which in December means a west wind carrying the full fetch of the ocean behind it. A windproof layer is not optional. The Parque Marechal Carmona (flat paths, resident peacocks, stone pines and palms) is the sheltered alternative if the seafront wind is excessive.
The Museu dos Condes de Castro Guimarães, a late 19th-century palace directly on the Cascais bay, provides the indoor option for a December afternoon. The restaurants on Rua Frederico Arouca serve Atlantic fish and seafood; in December the winter menu adds caldeirada and braised fish stews to the standard grilled options.
Nights Two and Three: Sintra
The Scotturb bus 403 from Cascais to Sintra takes approximately 30--40 minutes, running through the lower edge of the Serra and arriving at Sintra station.
The town centre and lower valley: The Palácio Nacional de Sintra at the top of the village - identifiable by its two enormous conical kitchen chimneys - is the accessible palace. It sits inside the town at a lower altitude than the mountain palaces, with flat interior rooms. Book entry at parquesdesintra.pt; arrive in the morning before the tour groups. The walk from the station is 15 minutes uphill; the Scotturb tuk-tuks and taxis outside the station cover it in minutes.
Pena Palace and the Moorish Castle are on the mountain ridge, requiring the Scotturb tourist buses (lines 434 and 435 from Sintra station) to reach the entrance gates. From the gate, both palaces still involve significant walking on uneven ground. Post-marathon Day Three or Four legs are better placed for this than Day One; if one of the Sintra nights is your first night after arriving from Cascais, leave the mountain palaces for the second day.
The Vila Sassetti gardens - a short walk from the station along the valley floor - are the genuinely flat alternative: a 19th-century estate with lower-valley paths through camellia and tree-fern plantings.
Monserrate Palace is accessible by the Scotturb bus 435 but the palace approach involves an uphill walk and the gardens extend over a hillside. Worth visiting, but with accurate expectations.
Sintra pastries: The shops near the Palácio Nacional sell the queijadas (cheese and cinnamon pastry) and travesseiros (puff pastry pillows filled with egg cream and almond) that are specific to Sintra. The Lawrence's Hotel - the oldest hotel on the Iberian peninsula in continuous operation - is in the historic centre, within walking distance of the station.
Return to Lisbon
Linha de Sintra trains run from Sintra station to Rossio every 20 minutes, 40 minutes. Rossio is in central Lisbon, accessible on foot to most hotels in the Baixa and Chiado area. Note: the loop exits at Rossio, not Cais do Sodré where it began - the two stations are 15 minutes' walk apart.