Cristo's first ever installation in the UK seem to be a different colour to their ends. It's not the case. This summer we learn what a mastaba is - a bench, originating in Mesapotamia. The temporary floating scuplture looks more like a decapitated pyramid or iceberg. Take your pick. With it's carefully planned minimal environmental impact is a giant something; part comment on global warming perhaps, part challenging building blocks - grown up lego, part, well, fun.