Aguas Livres Aqueduct

Lisbon spent most of the 18th century building itself a water supply, and the visible result crosses the Alcantara valley on thirty-five stone arches, the tallest of them pointed and over sixty metres high. The channel runs for kilometres from springs northwest of the city to a covered reservoir at Amoreiras, where the water arrived in a vaulted stone chamber that now stands empty and echoing. The great arches were finished before the 1755 earthquake and came through it undamaged, which locals noted at the time. On open days you can walk the pedestrian path laid alongside the channel, out over the valley with traffic far below and the arches marching ahead of you.

What you actually see

• The Alcantara crossing - thirty-five arches over the valley, the tallest well over sixty metres.
• The walkway - the pedestrian path beside the water channel, open on set days.
• Mae d'Agua reservoir - the vaulted arrival chamber at Amoreiras, now an exhibition space.
• The stone channel - the covered conduit itself, with inspection openings along the top.

When to go

Walkway access is limited and seasonal, usually with guided slots rather than open turnstiles, so check the schedule and book before travelling across town. Spring and autumn are best: the crossing is fully exposed, hot in summer and windy in winter. Mornings give clearer air over the valley.

Honest expectations

The walkway is closed more often than it is open, and plenty of visitors arrive to find a locked gate - the arches then have to be admired from the road below or a train window. The path is high, narrow and unsuitable for anyone with vertigo. The Campolide approach runs through a dull stretch of suburb.

Nearby

The Amoreiras reservoir and the Monsanto park slopes are both a short walk from either end.