Built on an islet in the center of the lake, the city of Mexico grew up with a network of canals and artificial islands, making the Templo Mayor take place. The Spanish conquerors built he Metropolitan Cathedral on top of it, so the memory of the old and imposing pre-Hispanic Temple was lost for centuries. In the late 70s, workers from the electricity company accidentally found structures that the archaeologists identified as the sought temple.
Fortunately, today you can visit a large dug up section in a good state of conservation. You can admire sections of the temples dedicated to Huitzilopochtli, the lord of war, and Tlaloc, lord of the rain. Between the walls of several sections of the temple, there are altars, snakes carved in stone and an imposing Tzompantli, which is a wall covered with representations of skulls, this because the Aztecs worshipped the dead, tradition maintained by Mexicans. https://www.visitmexico.com/en/actividades-principales/mexico-city/templo-mayor-museum