The part of Hattusa located at the foot of the Royal Citadel (tr. Büyükkale) is known as the Lower City (tr. Aşağı Şehir). It is also the first stopover on the designated Hattusa sightseeing trail. In this area, it is possible to see the ruins of the Grand Temple, the remains of an Assyrian trade colony, and the traces of residential houses and offices.

In this area, the traces of settlement date back to the predecessors of the Hittites - the Hattians. They lived here in the late third millennium BCE. At the beginning of the second millennium BCE, there was an Assyrian trade colony (Akkadian: kārum). Assyrian merchants established small colonial settlements next to Anatolian cities. Their most important export was copper, and import - tin and clothing. During the excavations in Hattusa, the ruins of houses and offices of the Assyrian merchants were discovered. The names of some of these merchants are known because of the tablets found there.

The Hittite houses, discovered so far in the Lower City area, surrounded a monumental temple complex. After passing through the gate, the visitors followed a wide, paved street with warehouses and a treasury, until they reached a water tank. It played a major role in religious rituals, just like another water tub located outside the temple area. This rectangular tub is known as the Lion Tub (tr. Aslanlı Tekne), because of carved lion heads at two corners. A surprising fact is that these lions have five legs each, just like the lions of Late Assyrians.

The Grand Temple (tr. Büyük Tapınak) stood in the center of the complex and was completely isolated from the environment as the admission inside was granted to the rulers and the priests only. This temple is the largest one in Hattusa, and is currently marked with number 1 for guidance. The temple was most likely dedicated to the supreme deities of the Hittites, derived from the pantheon of the Hattians - Teshub, the god of the sky, and the Sun Goddess of Arinna, in later times identified with Hepat, the queen of heavens.

The temple was built in the fourteenth century BCE. It was destroyed, along with the entire city, about 1200 BCE. The Grand Temple complex occupies an area measuring 160 by 135 meters, and the main entrance is on the southeast. Admission to the temple was also possible from the east, the west, and the south.

Only the wall base of the structure was built of large limestone blocks. Upon it rested the walls of a timber-frame construction, filled with mud bricks. These upper parts of the temple walls have not been preserved. However, it is possible to see many dowel holes that helped secure the timber-frame of the walls onto the stone foundations.

The temple had a flat roof sealed with mud. At the northeastern corner of the building there were two cult chambers. In these chambers, accessible only to the king, the queen, and the priests, stood images of the deities.

There were small rooms around the temple, used as warehouses. Large jars of various capacities, from 900 to 3,000 liters, were found in these rooms. They were used to store various liquids and foodstuffs, mainly wine, oil, and grain, as evidenced by the seal imprinted on them and other markings. In 1907, in the south-eastern area of the temple, archaeologists discovered thousands of cuneiform tablets. They contain the descriptions of religious ceremonies and other important information about the Hittites.

Some of the buildings outside the Grand Temple, in the Lower City, most likely served as the offices of officials and artists, and as their school. The other buildings were residential houses. They were constructed of bricks dried in the sun, laid on a wooden structure and covered with a flat wooden roof covered with mud. They had many rooms and were equipped with stoves and fireplaces, and sometimes even clay baths and sewer system.