Are you sure you don't mean the island's cave? You should always be able to enter the junkyard
Yeah sorry I meant the island cave, the first time I got there I was able to get through (to the junkyard) but now I can't anymore
Have you freed Tao?
No, I've never even seen him or the Rat King
Return to the junkyard's tunnel, leave the underground and explore the junkyard for more or less 3 times. If you have difficulties, click on the scroll icon on the bottom left, go to events log, Rat problem and follow the instructions