There are many possible places to use as a base in the region. I will share my thoughts on a few possible options. You can click on the name for the website to access the official tourist office websites for the official view. To find other local tourist office website the easiest way to search for “tz” and the name of the location, (e.g. tz vrbnik), TZ stands for tourist association in Croatian.
Rijeka is the third largest city in Croatia and very much the centre of the region. it is a lively city all year round, famous for its night life and for one of the largest carnivals in Europe, held in February each year.
Although certainly touristy in the summer Rijeka is not a major tourist destination like Split or Dubrovnik. It is a working city with shipbuilding and a large university. Its international claim to fame is that Rijeka is where the torpedo was invented. While access to the inlands involves either catamarans at inconvenient times or road trips, there are surprisingly good beaches within the city. The tourist office provides a useful guide to the beaches, and other guides to the city all available for download here.
Although not obvious at first there is a spectacular canyon virtually in the city centre. Despite being called “River”, which is what Rijeka means in Croatian, the river in the town is tiny, but comes from a deep hidden canyon. There is a path leading up out of the city from Titov Trg, or down from Trsat, into the canyon. The first hour is the most dramatic, the whole route to the source is about 25km. There is some rock climbing in the canyon, mainly close to the waterfall.
Most other hiking and running options usually involve a bus or train ride.
The city is well connected to Zagreb by frequent buses and slow trains. there are infrrquent buses to Italy and Slovenia. There are also buses to most places in Istria, the islands of Cres, Losinj, Krk and Rab as well as the rest of coastal Croatia. The buses heading south almost all take the coast road which is spectacular but slow.
Opatija is the original Austro-Hungarian resort on the Adriatic with grand old hotels by the sea. It is one of the few year round resorts in Croatia with conferences and seminars keeping hotels busy over the winter. Lovran is a smaller, and perhaps cuter, town just a few miles further down the road. Opatija is much less urban than Rijeka but is connected by the number 32 bus every 35 minutes – Opatija is in zone 3, Lovran zone 4. The Rijeka airport shuttle starts in Opatija.
The beaches are being improved but aren’t the best but it’s an easy walk, cycle, run, bus ride to better beaches in places like Icici or Ika. There are certainly plenty of swimming options in Opatija too.
Ucka mountain rises directly up behind the Opatija Riviera. there are paths starting in both Opatija and Lovran up to the summit – 1400m of ascent.
Krk is the main town on the island of Krk, which is connected b a bridge to the mainland. It has a beautiful historic centre. In the summer there are numerous tourist centres which are all relatively similar. Krk has the advantage of being the communication centre of the island with buses to all parts of the island and Rijeka which is convenient if you are relying on public transport. Unlike the other towns on the island it remains relatively lively all year round. A sunny day in winter attracts large numbers of day tripper from Rijeka.
Frustratingly there is no bus connecting Krk with the airport. The airport bus stops in Omisalj, just a couple of kilometres from the airport, from where it is possible to connect with the Rijeka – Krk bus. The same is possible in reverse or if you don’t mind walking about a mile you could ask the driver to drop you at the turning for the airport.
Platak is the main mountain centre in the Gorski Kotar. There mountain huts with restaurants open year round. This is the main ski area of Croatia since Bjelolasca closed. It can get very busy over weekends in winter when there is snow.