In contrast to the numerous investigations concerning the character and meaning of the Egyptian concept of the k3, there are few published opinions regarding the cult of the k3 which took place in the hw.tk3, the 'Ka-enclosure'. Archaeological and architectural studies of the only preserved royal hw.t-k3 of the Old Kingdom, that of Pepi I at Bubastis, are presented here. Using this evidence, the ... [Show full abstract] author attempts to ascertain whether, and to which extent, the construction follows the layout of other religious buildings, or rather, forms a type sui generis. The subsequent analysis of written sources referring to royal Ka-enclosures of the Old Kingdom allows the Bubastis installation of Pepi I to be placed in its wider context. Finally, die thesis of David O'Connor, who identified 6(th)-dynasty buildings discovered at Hierakonpolis and Abydos as royal Ka-enclosures, is examined and refused.