Quantum of Solace filmed at Piazzetta della Paglietta, Siena. M is targeted at the MI6 field base, whose entrance is this small square near Siena's main square. On screen it's MI6 field HQ.

Probable Named in published production coverage; the coordinate is the place itself, checked against a gazetteer.
Planning the trip? The Italy travel atlas covers money, language and getting aroundand everything filmed in Siena is on one page
Venture keeps every scene location on one map, sorted by how far you'd have to walk. Open it in Siena and it tells you what was shot around you, how to get there, and whether you can actually go in.
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