In short
Colombo is not Sri Lanka's destination, and it helps to know that: most travellers spend a night here on arrival or departure. The city is commercial, dense, and changing fast.
Fort is the colonial and administrative quarter. Pettah, right beside it, is the bazaar — dense, loud, organised by specialist streets. Galle Face Green is the great seafront lawn where the city gathers in the evening. Cinnamon Gardens is the leafy residential district.
Arriving and getting around
Bandaranaike international airport is some thirty kilometres north, linked by motorway.
Colombo Fort station is the country's real starting point. Trains leave from here for Kandy, the hill country and the south coast. Reserved-class tickets for the scenic runs must be bought several days ahead and sell out quickly.
Tuk-tuks are everywhere; insist on the meter or use an app, the price difference is significant.
What it really costs
Colombo is cheap, but more expensive than the rest of the country.
Seafront hotels and colonial addresses charge international rates; neighbourhood guesthouses are a fraction of that.
When to come
Sri Lanka has two offset monsoons, which complicates the season. For Colombo and the west coast, December–March is the dry period. The south-west monsoon hits this coast from May to September.
In practice there is always a dry region on the island: it is the itinerary that adapts to the season, not the reverse.
What nobody tells you
The train along the coast to the south leaves from Colombo and runs at the water's edge to Galle and Matara. It costs a few hundred rupees and is worth any excursion on sale.
The Pettah market is organised by themed streets — hardware, fabric, electronics, spices — and that is the logic to grasp in order not to get lost.
Colombo keeps traces of three successive colonisations — Portuguese, Dutch then British — visible in the architecture of Fort and in the street names.
Buddhist temples require covered shoulders and knees and the removal of shoes. Photographing yourself with your back to a Buddha statue is frowned upon and has led to prosecutions in Sri Lanka.