Decision. Two and a half days in Athens — the 08:00 Acropolis slot [1], the Acropolis Museum [2] and the Ancient Agora [3] — then one base for the remaining four nights, not two. Naxos is the default island [4]; a Nafplio-based Peloponnese loop is the better call if you want ruins and a car [5].
The single constraint that reorders everything is the wind. The meltemi blows June–September and peaks at 7–8 Beaufort in July–August [6], which is simultaneously the reason the Aegean islands sat at 28–30 °C during the July 2026 heatwave while central Greece hit 43.5 °C and the eastern Peloponnese 41–42 °C [7], and the reason high-speed catamarans get cancelled before the big Blue Star hulls do [8]. Comfort and connectivity trade against each other directly: the mainland tail never gets cancelled but bakes; the island tail is cool but the boat is a coin-flip. Neither angle can be read without the other.
Athens is smaller than a week suggests. The April 2025 ticketing reform put the Acropolis in its own €30 band and killed the combined ticket — buying the seven ex-combo sites separately now runs about €105 [9] — while Kerameikos has been shut since May 2025 [10] and the Odeon of Herodes Atticus closed in July 2026 for a multi-year restoration [11]. Fewer sites are worth paying for than a first-timer assumes. Two compensations this specific summer: the Parthenon’s west scaffolding came down permanently on 15 June 2026 [12], and the August Full Moon on Friday 28 August opens 126 sites free until 23:00 [13].
The transfer arithmetic kills two-island plans. Seven days minus an arrival and a departure day leaves five; each island change consumes most of one, and Cycladic guides want three nights per island minimum [14]. Only the Saronic escapes this — Piraeus–Hydra is 1h05–2h with 6–8 daily high-speed runs, and Hydra–Poros is 25–40 minutes [15]. That produces an unresolved overlap between two angles: the Saronic is simultaneously the best single day trip from an Athens base [16] and the only cluster where a genuine two-island tail works. You cannot do both — pick one.
The calendar is the live risk, not the budget. Peak-season guidance is to book 2–3 months ahead, 3–4 for August cabins and vehicles [17], and 15 August is Greece’s biggest domestic travel holiday, when ports pack out and ferries sell out outright [18]. Booking now for this month means the Naxos recommendation is only as good as its remaining availability — and the mainland tail, at €80–150 a room against €150–280 on Santorini or Mykonos [19], is the fallback that stays bookable late.
So the open question is not which island but how much ferry risk you are willing to hold: if the answer is none, the car and the Peloponnese win the week by default.