Good morning,
We are looking at a 2 week trip to Greece with our son and daughter in law in 2026. They have limited vacation time so the initial thought is a 7 night island cruise and 7 nights on the mainland. How would you spend or allocate the 7 nights on the mainland? I know there is a ton to see and do but their time is limited and the island cruise is a must for them (mid-30's).

Thank you!

What are your interests?
Archeological sites, medieval castles and settlements, folkloric danses, all kinds of museums, stunning landscapes, lakes, caves (with or without stalagmites), beaches, hiking trails, mountain climbing, modern cities...,......
Only if we know what you are looking for, we can give some useful advice.

There are an unlimited number of excellent possibilities. You can't go wrong! I can only share with you what I did:

3 nights Meteora. This was the sole purpose of our trip. We stayed at Doupiani House in Kastraki. It went beyond my already high expectations.
1 night Delphi.
Lake Vougliameni
Temple of Poseidon, Sounion Peninsula.
3 Nights Athens.

As neckervd notes, it's impossible to offer meanngful input without knowing the interests of those taking the trip. And as shelemm notes, there are many wonderful options.

Perhaps you will find some useful information in my trip report.
With Gratitude for a Glorious Solo Month in Greece

Certainly, more info would help.

I did Thessaloniki (visit Pella), Kastoria, Ioannina (visit Dodoni), Kalambaka for Meteora on the way to Athens.

Then I did a Rick Steves tour of the Peloponnese, the current itinerary is here.

But of course, if you want a couple of days in Athens, you will have to be very selective.

More soon in a trip report, but Meteora went way above and beyond our expectations.

Our trip is getting a little more focused. I am thinking we stay in Athens for 6 nights and do day trips to Delphi and Meteora. The first day will be recovery, then a day in Athens, day trip to Delphi, day to relax and poke around Athens, day trip to Meteora and then start the cruise. Rather than pack and repack, day long (and yes, I know they will be long days) are better suited to our little group.

The innAthens looks like a good hotel option. Has anyone stayed there??

Your trip, your call, of course, but FWIW, I would find daytrips to Delphi and Meteora unsatisfying and exhausting. And you are leaving yourselves very little time for Athens itself.