Driving on the main roads in the South Indian state of Tamil Nadu, the barely there villages that materialize every few miles take on a comforting rhythm: a handful of stucco cottages in mildew-stained pink, marigold and teal; a shrine to Ganesha on a tall white pole; a cluster of tiny thatched-roof stores, like packed closets flung open. On shaded porches in front, women in saris, shiny with perspiration, slice pineapple beside a glass-door cooler of Fanta.

Then, after hours, and with no warning, you pass an unmarked Rubicon, leading to an entirely different sort of outpost: the first in a cluster of 74 towns that make up the Chettinad region. Suddenly nothing you think you know about the humble, low-rise, rambling charm of rural India holds true.

Cement lean-tos and shacks give way to a formal grid of streets with mansion after looming mansion in various states of maintained opulence and elegant decay, their decorative facades partly hidden by high walls. Built between 1850 and 1950, these homes — some of which dwarf the grand cottages of Newport and the villas of Cap Ferrat — number over 15,000 throughout Chettinad, which covers about 600 square miles. Many have more than 60 rooms spread over interiors as large as one and a half acres. A trippy Walt Disney World of styles, there’s a Raj-inflected Victorian next to a Georgian Palladian with hints of Tudor, and down the street, an Art Deco confection straight out of South Beach.