Abstract: A natural way to study nilpotency in a group $G$ is to consider the colimit of the nilpotent subgroups of certain class. For a fixed nilpotency class $q$ there groups appear as the fundamental group of a certain subspace $B(q,G)$ of the usual classifying space $BG$, which are introduced in a paper by Adem, Cohen, and Torres Giese. I will discuss some properties of these colimits, and describe them for certain groups in the case of $q=2$ which corresponds to the colimit of the abelian subgroups.