This summer a group of eight of us spent 10 days in Istria, Croatia.

Istria is a beautiful peninsula in the west of Croatia. The area is made up of a mixture of fortified Roman towns, charming coastal villages & ports, and lush green countryside. 
The majority of Istria is located in Croatia but it does also extend northwards into Slovenia and Italy.
For centuries Istria was part of the Austrian Empire and then it belonged exclusively to Italy. The Italian influence in look and flavor is still present in the province.

Our base for the first three days was the city of Pula.  

As we arrived in the city we were immediately greeted by the magnificent Roman Amphitheater. Also known as the Arena of Pula, this Roman monument was built in the 1st Century AD at the same time as the Colosseum in Rome.  Although it was dark when we arrived the Arena was beautifully lit up and looked spectacular. 
The great thing about Pula is that it is easily navigated on foot and it is packed with interesting shops, bustling squares and quaint streets to wander.  It is also full of Roman monuments to explore.
A brilliant excursion to do from Pula is a boat trip around Brijuni Nation Park.  A delicious lunch was included on the boat and then we were dropped off for a few hours on one of the islands where we were able to swim and snorkel in the glorious waters of the Mediterranean.  
At night, while we were there, the city came alive, the streets and squares were packed with people eating and drinking, enjoying the cool evening outdoors.  And there was plenty to entertain the crowds, from musicians and magicians to flash mobs of dancers.

After three days we then traveled inland to the small town of Žminj were we had hired a villa for the next week.  While here we rented a car to explore more of the area (car hire is a must).

One of the wonderful places we visited was the fortified town of Rovinj, one of the most visited places in Istria.  
The Old Town is car-free and is a maze of quaint winding streets and alleys full of shops and galleries leading to the Church of St. Euphemia at the top.  The church is the largest baroque building in Istria and it is the highest point in Rovinj.  Visitors can climb the tower for an amazing view of the town and its surrounding area.
Also nearby is the protected Golden Cape Park Forest (Zlatni Rt), one of the most important parks in the Adriatic.  Teeming with thousands of plant species the park is great for hiking and cycling. 
There are also great beaches around Rovinj, including Lone Bay, Golden Cape Beach, Cuvi Beach and Golden Bay, although most of the beaches are rocky rather than sandy.

Other important towns in Croatian Istria include Poreč, Paxin, Umag, and Labin.  
Just over the border in Slovenian Istria visit the coastal towns of Izola, Piran and Koper.  Or go further north into Italy just south of Trieste.  All these places are in easy driving distance as it only takes an hour and a half to drive all the way from Pula at the bottom of Istria to Trieste at the `top.

Another day trip option from Istria is Venice.  Ferries depart from Pula, Rovinj and Poreč and take 2-3 hours.

Recommendations-

Riva Hostel in Pula.  This hostel is in a great location, as all Pula's sights are in walking distance, it has all you need facilities wise, and the price is very good.  We stayed here for the first three days of our trip and were all very happy with it.

http://www.rivahostel.com/

If you go to Istria in a group I couldn't recommend Villa Dino i Karla more.  The owners are lovely and very helpful.  And the villa itself is amazing.  Hiring a car for getting around is essential.

Villa Dino i Karla http://www.homeaway.co.uk/p871792