HS Graduation travel

Are you willing to rent a car? If so, stay in Athens when you arrive. You don’t want to drive after a night of no sleep.
The Peloponnese Peninsula is where you want to go. Focus on Olympia, Mycenae and Epidavros for history and Nafplio for the beach. Nafplio is also a good base if visiting Mycenae and Epidavros.
From Nafplio you can drive to Olympia, then the Mani Peninsula and Monemvasia depending on how much time you have. You can drop off your rental at the Athens airport and sleep at the Sofitel hotel the night before you fly home.

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The girls are interested in art, food, history, and the water

In Greece there are hundreds of museums in all possible arts, historical/archaeological sites, around 200 visitable islands, at least 20,000 beaches on more than 16,000km of coastline, and its food is known throughout the world.

With only 8-10 days it will be necessary to make a drastic selection

It takes at least 3 days to partially visit Athens.

Whether on the mainland or in the islands, do not make the mistake of selecting places to visit without taking into account the distances, transport possibilities and duration of journeys.

In Greece the minimum age to rent a car is 21 (often 23 to rent a scooter or ATV), and a driving license valid for more than one year is required. Additional fees apply under 25

Priorities: Safety, memories, budget. Any advice?

Greece is a very safe country, even for young women

In May/June it is very easy to find accommodation for less than €80/night and to eat very well in a restaurant for less than €15/person including drinks. There are a few exceptions like Mykonos and Santorini which are extremely expensive islands.

For the best weather AND Best budget, we "vets" highly recommend going last 2 weeks in May (crowds and room prices go up in June). Water is "brisk" for first 20 seconds then blissful... weather between 70 -- mid-80s. If coming from N America (tip: for best advice, say where from). Trip length: 8 is NOT enough -- even shortest travel (nonstops from E Coast leaving 4pm on) you arrive from 9-noon next day... and you can't count departure day at all... so that means only 6.5 days. If you pick flight w change in Europe, you lose most of Day 1, so just 6. Recommend shortest trip: leave on a Thurs nonstop Thurs night, return on 2nd sunday = 8.5 days. This is STILL very short, since since you have ample time, study up & strategize. (& booking 6 months ahead = budget savings).

Agree that Peloponnese is excellent for short visits like yours -- accessing best-known islands takes precious time, even when you do domestic flights (costly). If you've had a loooong journey, u can get a nearby hotel on a beach for 1 night, to recover jet-lag, then shuttle back to airport early rental car, then zoom off on (modern) intercity highway to beautifuL NAFPLIO (this fab online map shows the Athens-avoiding route). https://tinyurl.com/zekuft9 (clilck & it gets huge). Gorgeous town on a Peninsula (considered the most beautiful Old Town in all Greece), has it all -- surrounded by ancient sites, has amazing architecture, cafes, msuems -- and an array of beaches -- this (noncommerciall) website tells all; clilck every lilnk! http://www.visitnafplio.com/ YOU can visit ruins and castles galore, with swims, and the best sunsets in Greece iMHO. After 4 days there, you can drive back for 3 days in Athens & its famous landmarks.. Allows for a stress-free trip with great variety.

PS Do not get brainwashed with youtube "eye-candy" about famous-islands... getting there & back eats up precious days, and avoiding cruise=ship crowds & package tour throngs will eat up your budget too.

Thanks so much! I will look at trying 11-12 days instead. I appreciate your input!