It’s hard advice to give in Lisbon, considering every inch of the city is covered in black and white cobblestones. Hint (from someone who’s tripped, slipped, and fallen many times in Lisbon): the white stones are the most slippery, and the more polished they look, the worst they are. And, yes, that means the harder the fall.
Although I love the patterns of calçada portuguesa, they are dangerous. There’s a whole debate on this, with one side wanting the pavement to become cultural heritage and the other side defending it’s time to let it go considering how risky it is, particularly for people with reduced mobility.
But if you can’t avoid the sidewalks in Lisbon in the rain, at least avoid the shiny, all-white squares like, for example, Praça do Comércio.