The Trang An area consists of Trang An karst massif, low hills and adjacent accumulation landforms belonging to the Southeastern part of the Hanoi plain, The Trang An landscape complex lies entirely in the Trang An karst massif, and is composed of pure and fairly thick limestone of the Dong Giao formation (T 2a dg). It is located in an area of continuing slow neotectonic uplift. This area is also the SE extreme of the mountain ranges belonging to the Paleo-Tethys ocean branch, extending to Viet Nam from the Southwest. After creating the famous Northwestern plateaux, this limestone range extended through Cue Phuong to Trang An, where it was dissected in a lattice form with narrow bands of limestone alternating with closed and open valleys, then it formed isolated karst towers scattered on the plain before plunging fully beneath the plain which extends toward the Gulf of Bac Bo. Formed 250 million years ago and undergoing a very mutative geologic history, especially the subsidence of the East Sea, the expansion of the Hanoi trough, sea transgressions and regressions, the Trang An limestone massif comprises numerous classical tropical karst landforms including cones, towers and unique transitional forms. These landforms have a logical sequence from the outer margins towards the centre: from the oldest on the plain to younger in the transitional area, and the youngest at the centre. Especially, between the transitional area and the margins is a true karstic bay lands cape that has become "fossil" - emerging above the sea level. Although the sea has gone away from Trang An for thousands years, the "karst landscape invaded and transformed by the sea" is still preserved with karst hills, karst towers and cones bearing traces of the former activities of the sea, such as sea level notches, abrasion terraces, through caves, tidal lakes, flooded valleys, bizarre shapes created by karst process, arc-shaped karst "ramparts", sword-like features that are found nowhere else in the world. Together with the outstanding historical and cultural values, the natural landscapes of Trang An complex have super geomorphologic and aesthetic values, deserving the inscription in the World Heritage list under UNESCO natural and cultural criteria.