The ruins of Castell del Rei are in Pollença, on the Tramuntana coast. The entrance gate can be seen in the lower-left part of the image. Higher up are several battlements and a section of wall with another gateway. The postcard is dated around 1930 and is credited to N.C.P.
Source: N.C.P. Ca. 1930
Archive: Andreu Muntaner Darder