Large crosswords 21x21 with richer vocabulary

A 21x21 grid is one step larger than the standard format, the field leaves more room for a richer word selection and allows rarer vocabulary that simply doesn't fit into the smaller formats. This is the format people move to once the standard size starts to feel too easy, but the marathon of the largest grids, usually solved over several sessions, isn't quite within reach yet. At the same time, a 21x21 can still be finished in a single sitting, just a longer one than the smaller formats need.