Amymone and Poseidon are one of the less known couples of the ancient Greek mythology. Poseidon, god of the sea, earthquakes and horses was, as we all know, happily married to Amphitrite, but, like all gods, had an occasional affair every once in a while.
Amymone was one of the daughters of King Danaos, which meant that she was a Danaid, and also that she had 49 sisters at home. The funny thing about Danaos having 50 daughters is that his twin brother, Aigyptos, had 50 sons. Long story short, Aigyptos wanted his sons to marry their cousins, Danaos didn't, so he took his girls and fled.
Danaos and his daughters found shelter in Argos, where the people had only good intentions, but were in serious trouble, because the entire region was dried up. That severe drought was Poseidon's doing. He and Hera competed for the supremacy over the new city, and Hera won. Poseidon decided to avenge his wounded ego by making the locals die of thirst.
The newcomers tried their best to help, and all the 50 daughters of Danaos went in search of water. Amymone went deep into a forest, hoping to find a spring, but instead, she stumbled upon a satyr, who was instantly charmed by her looks and attempted to rape her. Amymone's cries and shouts attracted the attention of Poseidon, who saved her from the satyr and kept her for himself. Before letting her go, he showed her the location of the springs of Lerna, so the region was saved.
Amymone and Poseidon had a child together (that's generally the whole point of these stories when a god mates with a mortal) named Nauplios, who was the grandfather of one of the Argonauts. Amymone did eventually marry her cousin, specifically the one named Lynceus – and was the only one to do so, as her 49 sisters killed their 49 husbands on the wedding night, but that's a different story. The children Amymone had with Lynceus started a long line of kings, which would culminate with Danae and her famous son, Perseus. Don't you just love how everybody is related to everybody? Just like a soap opera.