It is shown that the hyperspace (resp. ) of non-empty closed (resp. closed and bounded) subsets of a metric space (X,d) is homeomorphic to ℓ₂ if and only if the completion X̅ of X is connected and locally connected, X is topologically complete and nowhere locally compact, and each subset (resp. each bounded subset) of X is totally bounded.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-cm113-2-4, author = {T. Banakh and R. Voytsitskyy}, title = {Characterizing metric spaces whose hyperspaces are homeomorphic to l2}, journal = {Colloquium Mathematicae}, volume = {111}, year = {2008}, pages = {223-229}, zbl = {1155.54011}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm113-2-4} }
T. Banakh; R. Voytsitskyy. Characterizing metric spaces whose hyperspaces are homeomorphic to ℓ₂. Colloquium Mathematicae, Tome 111 (2008) pp. 223-229. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm113-2-4/