Which City Is Farthest from London: Sydney, Madrid, or Cairo? Sydney — 17,000 km

Sydney is by far the farthest from London.

Great-Circle Distances from London (LHR)

• Sydney (SYD): ~16,980 km (10,550 mi) — ~22 hr flight
• Cairo (CAI): ~3,500 km (2,175 mi) — ~4 hr 45 min
• Madrid (MAD): ~1,260 km (785 mi) — ~2 hr 30 min

Why the Huge Gap?

• Sydney: Antipodal to London's "opposite" — nearly opposite sides of Earth.
• Cairo: Same hemisphere; Mediterranean/N. Africa.
• Madrid: Neighbor; Western Europe.

Context

London–Sydney is one of the world's longest commercial routes (Qantas PER-LHR nonstop 17,000 km; SYD-LHR requires stop). London–Madrid is a short hop; London–Cairo crosses Med + Sahara.

Answer: Sydney.