First reflex when the sky darkens: check where it's actually raining. Mauritian rain is often very localised — it can be pouring in Curepipe while Flic en Flac bakes in the sun. Check the Vacoas weather station radar, jump in the car and switch coasts: a 40-minute drive is often enough to find blue sky again. If the whole island is soaked, don't panic, the rest of this guide is for you.
Head to Port Louis first: the Blue Penny Museum at the Caudan (Rs 275, closed Sundays) houses the world's most famous stamps, and the UNESCO-listed Aapravasi Ghat tells the moving story of indentured labourers — free entry, allow 1h30. Follow up with the Caudan Waterfront shopping arcades, its covered craft market and a vanilla tea under the multicoloured umbrellas of the iconic street.
L'Aventure du Sucre, in Pamplemousses, is arguably the island's finest museum: a former sugar factory telling 300 years of Mauritian history, with a tasting of special sugars and rums included (about Rs 550, open daily 9 am – 5 pm). In the same spirit, the Chamarel Rum Distillery and the Bois Chéri tea factory can be visited in the dry, tastings included — rain on the tea bushes is actually rather photogenic.
With children, head for Odysseo in Port Louis, the Indian Ocean's largest oceanarium: 45 tanks, a shark tunnel, around Rs 700 for adults and Rs 450 for kids. Otherwise, the food courts and cinemas of the Bagatelle, Phoenix or Cascavelle malls will happily fill an afternoon — Mauritians themselves spend their rainy Sundays there.
Last option, the most local one: use the time to cook. Several tables d'hôtes and guesthouses offer half-day Creole cooking classes (Rs 1,500 – 2,500, curry, rougaille and chutneys on the menu). You'll leave with recipes, laughter and the guarantee of never ruining a chicken curry again. Local tip: a downpour rarely lasts more than an hour — order one more dholl puri and wait it out.