I got a strange question on earthworms..can someone please help me..?

I am in Malaysia,a tropical country with many exotic plants and animals.Just like the West,we too have our strange insects and also small little worms. Now this is the interesting bit.I live in a township.Considered to be Urban. The best part is i live in a shop lot.It is very popular in Malaysia,where there are shop operating at the bottom and you could have residents living at the top.I am living at the most top floor.Meaning i am on the 3rd floor. Below,there are just tarmac roads.

The strange thing is this,i have earth worms living inside the tiles of my toilet.they will ocasionally bask themselves out.I have lived here like for 10 years and nothing like that has ever happened.My question is,how did these guys get here????I mean,there is no trace of earth,within a height of 30ft from the ground.I dont keep plants.Even if there were,like i said,i am located about 30 ft from the ground.Whose road is tarmac.These worms are nothing small.I have caught one previously and it was about 3-6 inches long.And the wiggle out of the tiled floor.There are a colony here i suspect.I mean to some extent,i find it irritating sharing my bathroom.What is more irritating,is that they appear out of nowhere.Could someone help explain this?