So i just remembered this book i had read a long time ago and i cant remember its name, all i know is that the premise whas that this kid that had heart problems went to his grandmothers house for the summer and he found this thing in her attic that transported him to some place where his heart problems and asthma disappeared he got found by some old guy that told him he had traveled through what they called the fold and he helped him learn how to fend for himself. And i think this main characters name was aster or something like that. Any help or even other reading suggestions based off this would be awsome.