Getting to the heart of the domain wasn't exactly simple. He had to consistently check with Leroy to see if he hadn't accidentally teleported past it. But, at a certain point, Lex was able to tell on his own where the heart was.
It started with entering a bog that gave off a noxious gas that was both corrosive and poisonous. Of course, it did nothing to Lex, but he could see how anyone else would have been highly inconvenienced if not completely deterred by it.
The fact that the bog also contained countless venomous beasts was also a strong indication that they were close. By this point, Leroy was already deeply invested in sharing the troubled past of his people, so Lex felt slightly awkward disturbing him, so he continued on his own.
