Bohemian Forest
They create a natural border between the Czech Republic on one side and Germany and Austria on the other . 
<triplet> Czech Republic <subj> Germany <obj> shares border with <subj> Austria <obj> shares border with <triplet> Germany <subj> Czech Republic <obj> shares border with <subj> Austria <obj> shares border with <triplet> Austria <subj> Czech Republic <obj> shares border with <subj> Germany <obj> shares border with