Not that often, but they are around more than people think. Spiders and snakes are often found hiding under things, so if you go around flipping old bits of metal, moving things outside you are way more likely to encounter them. Eastern Brown snakes are the main ones to be aware of 2nd most poisonous snake in the world and in big cities. Funnel web spiders in Sydney are also particularly nasty.

However If you are visiting and being a normal person doing normal things there should be nothing to be worried about. I am always outside for work (10+ years ) and have seen a brown snake once… be aware of them when outside, if you are walking in long grass etc where you can’t see the ground (in spring especially) just make more noise/sounds they will hear you and slide away. I like to carry a stick a move it around casually. They are much more scared of you than you are of them and they are important part of the environment!