As suggestions for best type of shoes for exploring all over Greece. I'm told there will be lots of walking and stair-climbing, etc. Are athletic shoes appropriate or would Merrills be better?

Try on some Keens! I love their excellent traction, support, quick-dry and anti-smell features and they are fine for hiking, too- I wore mine for the CT. I liked that traction on all kinds of boats (if you are going to the islands)and slippery stairs. On the other hand, if you will have more little pebbles on hiking trails than stairs, you might try the more enclosed models. That said, I only had to stop once to fish out a small rock with the sandal style...

A good cross-training shoe intended for rougher terrain (like some Merrils) is a good all-around for Greece, especially if one is visiting the archaelogical sites, doing some light hiking, etc.

I especially enjoyed exploring slightly off the beaten path, and next time will likely bring along high-top, lightweight boots (eg, Lowa GTX). But I would also pack either sandals and/or lowcut athletic shoes, sometimes even the very-light hike boots get a bit burdensome.

Unless you will be doing some serious trekking, Merrils are probably overkill. I usually wear Tevas in Greece, even for walking around. There are some types of sandals specifically designed for hiking, and if chosen carefully are cool and comfortable. For any type of footware you will be doing lots of walking in, wear them at home before setting out on your trip.

I'm with Heimdall. Hiking boots are probably over-thinking it; and heavy to carry. You fail to say what time of year, also -- that affects advice. I have done well in may/june with heavy-duty athletic shoes (i.e., thick soles, not Keds), climbing up mountains, walking down Imbros gorge, climbing up to Ancient Thira, walkng up to 5 miles at a stretch, and I'm no kid (alas).

Heimdall - "Merrils are probably overkill "

A cross-training shoe being overkill ??? We must have completely different shoe models pictured in our minds.

Tom_h, Merrills make lots of different shoes and boots. The OP asked "Are athletic shoes appropriate or would Merrills be better?" I assumed, rightly or wrongly, that meant heavy duty hiking shoes, or she/he wouldn't have made the differentiation between Merrills and athletic shoes.

As a matter of fact, I am wearing a pair of Merrills at this very moment I wouldn't even use for running, much less for a long hike. They are just comfortable casual shoes that would be fine for Greece. I'll be bringing my Tivas for wear during the day, and also something that covers the foot for evenings, to keep the mossies at bay.

My family and I went to Greece for a little over two weeks last June. My 19 year old son wore his Adidas tennis shoes everywhere. My husband wore Mephisto sandals and I wore Wokky sandals for all the touring. We were on every type of terrain there was including a ship.
Have a blast! (I'm going back this June
--can't wait.)