Heiligenstadt: Red Vienna and the kilometre-long courtyard
The kilometre-long social-housing superblock of Red Vienna, the Hoffmann villas, and the canal below. This is a Claude-drafted route awaiting the editor's walk.

1. Heiligenstadt (U4)
Step out of the U4 and the *Karl-Marx-Hof* is right there across the road — you can't miss the great ochre-and-red front. Cross over and start at the famous arched gateway.

2. Karl-Marx-Hof — the great arches
The flagship of Red Vienna: a kilometre-long block of 1,300-odd flats, built 1927–30 by Karl Ehn, with four monumental arches over the main facade. Stand under the central arch and look up; the scale is the argument the city was making.

3. The inner courtyards
Walk through into the courtyards behind — green, calm, more garden than estate. The point of the building was light, air and space for working families; in the courtyards you see the idea, not just the front. People live here, so tread lightly.

4. Heiligenstädter Park
A short green breather between the housing block and the villa slope. Benches, old trees, a place to reset before the climb up to the Hohe Warte. Skip it if you're short on time; linger if you're not.

5. Hohe Warte villa colony
Up the slope, a cluster of villas Josef Hoffmann designed around 1900 for artists and patrons — the other Vienna to the *Hof*'s collective one: private, refined, *Secession*-era. The Moll-Moser house is the set's keystone. Quiet residential streets; look over the garden walls.

6. Down toward the Danube canal
Drop back east toward the *Donaukanal*, the tamed arm of the river along the district's edge. The waterside path is the easy way back; turn south on it and the U4 at Heiligenstadt is a short walk along the water.

Heiligenstadt: Red Vienna and the kilometre-long courtyard