Hi. Looking to do a day trip from Athens to an island or two with my husband and twin 13 year olds. I am wondering two things... 1) What island do you recommend from Athens? I am leaning towards Hydra as it is car free but have read that Aegina and Poros are also good options. 2) I would rather not do this on a tour and take the ferry ourselves so we have some flexibility with our timing. We will not have a car and plan to 'walk on'. We will be travelling in July. Will we need to prebook our tickets on the ferry?
Thanks for your help! I am so excited!
Tanya

Hydra is lovely and has some nice hikes but not known for its beaches so factor that in if important. Ferries are regular (one with open deck). We just bought tickets at the port but in July I’d be tempted to buy tickets a day or two before, just in case, but I’ve never visited Greece in July so not sure.

Aegina probably has the most things to do that might be of interest to visitors. Passed by Poros on the ferry and what we saw looked lovely but don’t know more other than what I’ve seen on the internet.

If not staying long I’d also consider travel time.

I just answered a similar query on another forum for family with 3 teens, so I'll cut & paste (with corrections):
First, let's deal with Hydra... it is constantly promoted by sites like Rick Steves (because his tours promote it) and because it once was favored by celebrities. Problem for me, is, it's mainly about the pretty harbor, & you have to hike to beaches... the other 2 islands don't have that much traffic except weekends, and there's more for Teens on Aegina, in my opinion. Poros, according to my Athens friends, is more a Greek thing... like the Jersey Shore (those who go there every year as children love it, others wonder what the fuss is about). And both of these take longer, and on inside-seating ferries only.
I would suggest Aegina... because it's closest, yet gives you a 1-hour "mini-cruise" if you catch the right ferry -- an open-deck big ferry where you can sit out & enjoy seascape -- huge freighters & cruise ships, speedboats, 3-masted schooners & tiny sloops. Avoid hydrofoils; you're stuck inside, salt-rimed windows, no view. Try to get a 9 or 10am open-deck ferry. When you arrive, by tickets for an INbound open-deck ferry around 6, 7 or 8 pm, maybe enjoy a sunset sail.

Aegina has a limited local bus service but with 4 of you, renting a car on arrival is probably a good buy, But if you like "biking with an assist" I've learned they now rent e-bikes, Yay! with e-bikes, it's an easy ride to high point of Island -- Gorgeous temple ruin w 360° view of entire Saronic bay. Gorgeous! GIve it 15 minutes... then scoot downhill to Ag Marina beach for swim & lunch. With a car, you can explore a litttle further (do a bit of homework -- https://athensbylocals.com/one-day-t...aegina-island/) When you get back to port, wander some back-streets (not touristy), fun to check out the shops used only by locals. Then have ice cream & drinks at a portside cafe & do open-deck ferry back to Piraeus.Here's a great photo-album of june day-trip --