Good morning - I'm planning a summer vacation with my 2 sons (21/18), my wife and my niece for 16 days. I'm set on Istanbul for 5-7 days but struggling for a second location to visit. I'm thinking Isreal but also Greece or other locations within an hr or so flight. We enjoy site seeing and architectural/art but also open to some beach time especially if there's good snorkeling. Look forward to any recommendations - thank you.

Turkey has a wealth of options! You might start by looking into extraordinary Ephesus or the various options around Antalya. Here's my old trip report:
Some Observations on a Fantastic Journey through Western Turkey

If you visit Istanbul for four days, Cappadochia for another 3 days or so , and a day or two in Epheseus you would have a week or so to spend on a gulet enjoying swimming, snorkeling and exploring. I have done the first part of the trip I mentioned above and have friends who added a gulet trip which they thoroughly enjoyed.

KTtravel's suggestion is spot on!
Cappadocia is amazing!!!
Ephesus is interesting and quite beautiful.

Spend the whole time in Turkey. It is a wealth of glorious architecture, a huge variety of landscape and wonderful food.

A gulet trip sounds like a good idea. There are some beauriful beaches on the Turkish coast, but the towns themselves aren't that memorable. (Bodrum and Alaçati being the exceptions) The rest is overdeveloped.

But bear in mind that southern and central Turkey can get extremely hot in summer. (40°C)
I'm not sure you would enjoy visiting Cappadoccia or Ephesus during that time.

Or you can visit Istanbul for 4 days then spend 10 days island-hopping in Greece. There are cheap flights betweem Turkey and the Greek islands.

Long ago I went to Ephesus (ancient Troy) from Istanbul by bus - really enjoyed the ruins there (loackerwafer did too!) and then took a boat from nearby port over to the nearest Greek island - Cos or whatever and yes island-hopped by boat towards Athens - some boats go overnight with cabins, etc.

LOL PalenQ. For the record, I love Ephesus. Very impressive. But I think sightseeing in Southern Turkey in July/August can be really unpleasant.

By the way, the island you're referring to is Kos. Symi is also not far from Ephesus.

Ephesus is not Troy, and it is close enough to the coast that if one can take coastal heat, one can probably take the heat in Ephesus.

We spent three weeks in Turkey and it certainly wasn't enough. I concur will all those above about Cappadocia, one of the oddest places we have visited.

I wasn't so enamored with Cappadoccia, myself. Pointed rocks! Big deal.

Oh, yes! Do consider including 3 or 4 days in Cappadocia!

And as Michael notes, Ephesus is NOT ancient Troy.

Oops don't know why I said that but for some reason thought that even though I was there - thanks for correcto. Maybe it was ancient Troy I visited from Istanbul - twas a long long ago.

thank you all for the fantastic suggestions - very much appreciated !!