On display in the first floor os the Lazaros Koundouriotis Historical Mansion are watercolors and oil paintings of large dimensions with Hydriote subjects, donated by the artist himself.

Tetsis was born in Hydra in 1925 were he lived his childhooh. He studied painting in Athens and Paris. He was a founding member (1958) of the School Vakalo and a teacher until 1976. From 1976 to 1991 he was a teacher in the Athens School of Fine Arts. In 1993 he was elected a member of the Academy of Athens. He died in 2016, in Athens.

Tetsis was an exponent of the post-impressionistic seascape tradition.