Hades and the River Styx - Ancient Greek myth
When your soul reached the River Styx, a boatman named Charon would give you a ride to the underworld. But the ride was not free. If your family had not buried you with a coin to use as payment, you were stuck. Some souls, who did not have a coin, tried to swim across the River Styx. Some made it. Most didn't.
For those souls who received a ride in Charon's boat, or managed to swim across the river, there was little to do on the other side except wait to be reborn into a new body. These souls would not remember their prior life. They would start over as an infant. So, unlike the ancient Egyptians, the ancient Greeks didn't spend a lot of time planning for their afterlife because they did not expect to be there very long.
According to Greek mythology, some people were shocked to discover that they would be stuck there for some time, in some cases, forever. Some souls were sent to the Underworld as punishment. For others, it seemed to take quite a while to find just the right body. The Underworld was not packed, but it was populated.