The text above the first image is in both Greek alphabet and in English, the latter being:
(He did did not seem to be resting, but his mind was in action and he seemed to be revolving some subtle plan ...)
More on the background of the Palatine Anthology and it's significance is available here (pp 362)
The Palatine Anthology was discovered in Heidelberg in 1606, and is a collection of approximately 3700 epigrams, or poems, derived from the collection compiled by the Byzantine protopapas (archpriest) Constantine Cephelas around 900 AD.
The second image is of the Lion Gate in Mycenae:
and is accompanied by a poem fragment that is attributed to the Greek Anthology, which is the collective title for the Palatine Anthology and the smaller Planudea Anthology.
The text underneath the first image translates into English as Archaia Epidavros, the current name for a small fishing village at the east coast of the Peloponnese.
The text above the price on both stamps translates into Latin lettering as Eisithirion, the Greek word for ticket. (Observe also the perforations along the left edge of both images.)
OP's guess that they are museum tickets might explain the dual Greek/English wording.