"Hadst thou sought the whole earth over," said he, looking darkly at the clergyman, "there was no one place so secret, —no high place nor lowly place, where thou couldst have escaped me,--save on this very scaffold!" (23.18)
The only place for Dimmesdale to escape Chillingworth is in public. Ironic, right? Hiding out, escaping to England, living in the forest—anywhere he tried to hide, Chillingworth would find him. But the moment he casts off his hypocrisy, he's free.