Chiesa di San Zaccaria

San Zaccaria, just behind the waterfront near St. Mark's Square, holds one of Venice's strangest and most atmospheric spaces: a submerged Romanesque crypt where eight early doges lie buried beneath water that rises and falls with the lagoon's own tides.

The nave is free and the crypt, sacristy and choir carry a small combined charge of a few euros. Given that the crypt is a waterlogged 10th-century structure requiring constant attention, this is one of the more obviously well-spent admissions in the city.

The crypt floor is wet, uneven and genuinely slippery, and the duckboards are narrow. It is not suitable for anyone unsteady on their feet, and there is no shame in looking down the stairs rather than going in.

San Zaccaria is an active parish and the neighbouring buildings are a working Carabinieri barracks -- the campo is not a place to picnic, and photographing the convent side rather than the church is unwelcome.

Because it sits so close to San Marco, this is one of the genuinely useful pressure valves in the city: an hour here takes a visitor out of the worst crowding in Venice without moving more than a few hundred metres.

The church itself is free to enter. A small separate fee, around 3 euros, covers the sacristy, the choir stalls, and the flooded crypt -- worth the extra cost for anyone curious about the building's oldest and strangest space. San Zaccaria is a short walk from St. Mark's Square, just behind the waterfront.