The Greeks had a lot of myths this influenced their culture a lot. For example lot of Greek myths have some thing that has multipile heads. Where they got that was proply from from twins where one of them died and the other twin had that twins head and his.The idea about the underworld could have come from them finding skelitens in caves and they thought that since they didn’t like to live in caves maybe those people had been punished by the their gods. It also could have been some hero fought some monster like a dinosour or a bear or some other creature.
The ways they were influenced by these myths can be seen in the Olimpic games as they wanted to honor their gods who were sometimes part of this amazing stories. It can also be seen on their pottery as they would sometime draw pictures of these myths on their pottery.