Bijapur
The Gol Gumbaz — the mausoleum of Adil Shah II — sits in your memory long after you've left Bijapur. Its central dome, measuring 44 metres in diameter, was the largest in the world for centuries after its completion in 1656 and remains the second largest unsupported dome on earth to this day. But the real star is the 'Whispering Gallery' running inside the dome's base: even the faintest whisper travels across the entire 37.9-metre diameter, a piece of 17th-century acoustic engineering that still astonishes visitors.
Visit on a weekday morning — the Whispering Gallery effect is completely ruined by crowd noise on weekends. The museum inside the gateway is worth 30 extra minutes.