Yes, I am traveling to Thessiloniki , Greece in early April to attend a festival. I was wondering what interesting islands are easily accessible from Thessiloniki. Also can you tell me some interesting sites to visit in northern Greece.
Don't miss the big archeological museum when you're in Thessaloniki. Rick's guidebooks don't cover this part of the country, so I used Lonely Planet (and a rental car) for the mainland. Nearby beach destinations on the mainland will still be pretty dead and may not have bus service.
You can reach quite a few destinations by nonstop flight from Thessaloniki. At www.skyscanner.com, you can search from Thessaloniki to "Greece" to get a list. On various dates, these may include Rhodes, Crete, Mykonos, or Santorini. (Also Kos but it's not at the top of my list.) Or go straight to Aegean Air, which probably operates most of them.
Pella, Vergina and Edessa are all worth visiting and can be done on a day trip. We’ve written up our experience of doing this, and some other places we visited in Thessaloniki here.
Unfortunately the site is not (yet) mobile friendly so you’ll need a PC or tablet.
Skopelos is the nearest island to Thessaloniki but is still three hours by ferry. The Halkidiki peninsular is reachable by bus and has nice beaches and forests.
Pella, Vergina, Dion are all great archeological sights to see not too far from Thes/niki.
The lake north of Thes/niki is a bird sanctuary if that is of interest.
Not an island, but you will find archeological sights on the way to Halikidiki. The first peninsula, Kassandra, has spectacular beaches and great seafood restaurants. Porto Fino is one of the large, high end resorts there.
The second peninsula is greener (in a literal sense) and has many eco-friendly places to stay with relaxing beaches. All this to say that you may find what you are looking for in this area without having to spend time traveling to an island further away.