by XERXES COOK Anybody who has lived in a city will know that feeling of being there too long. Especially if that city has winters as miserable as London’s. So, feeling the need for a change of scene, and for a bit of a scene, last February I booked a trip to Tulum. I was curious as to whether my Instagram-incubated expectations of lunches at Coqui Coqui, meditating in the sound bath of Uno Astrolodge, and swinging in the palm-fringed hammocks of Nomade were worth all the fuss. And they definitely are, but here I’m going to get super-fussy: scoping out people like me queuing in the midday sun for a dinner reservation at Hartwood, next to shops selling simple crochet-knit dresses for $250, I couldn’t shake the feeling that Tulum is to hipsterdom as St. Tropez was to Brits in the Agatha Christie-era. It’s not a place to escape…