Same as they do in a house or office
RATS
sewers
You can buy cheep fuzzy rats in the sewers
Actually, the sewer people mate with rats to make Ratmen, who then live in the sewers. So, there is more ratmen.
Because there's garbage, water, shelter, and safety in sewers. What more could they want?
You can find these Hell Rats in the sewers in Varrock, You can find Varrock by exploring your map, have fun.
rats, garbage, poop
You can often find rats living in sewers, but that's not the only place they live. They can also live on the streets, especially dirty areas, in the country, in homes.. basically anywhere. Eww..
Giant rats can commonly be found in sewers and drainage systems throughout the city. These are common homes for them as they are secluded from humans.
Garbage dumps, sewers and anywhere they can find shelter away from the eyes of people and other predators.
The Bubonic Plague otherwise known as black dealth was originally spread by a type of insect I believe similar to a mosquito. In Asia, around India, has a huge collection of rats and the disease was passed to the rats. Rats then got in sewers and other commonly used places by Europeans and so they got the plague
The sewers of London were built because at the time London was a stinking place were people were dying of preventable diseases. The father of modern railways talked the government into financing the building of sewers to remove the sewerage building up on the streets. As a bonus though when the sewers went in the scale of disease in ordinary Londoners dropped very quickly. No sewerage, no rats, no smell, no worries