A modem city has been set up in -what-was a wasteland ten ye

in 后面缺少一个宾语从句,宾语从句中又缺少was的主语,在名词性从句里,缺少主宾表的时候,可以考虑一下what.这句话里what 可以转化成the place which.
再如：The school library was built in what used to be the children's playground.
= The school library was built in the place which used to be the children's ...