MC Escher Balcony (1945) in Lego:

MC Escher Relativity (1953) in Lego:

MC Escher Belvedere (1958) in Lego:

MC Escher Ascending and Descending (1960) in Lego:

MC Escher Waterfall (1961) in Lego:

I think the originals were made by Andrew Lipson (www.andrewlipson.com), but his website has been down for ages....