The region has huge mountain biking potential. Most routes are not particularly technical but are in wild and often isolated areas. There are a range of resources for information on routes.
Local tourist offices all advertise mountain bike routes and often have maps of routes in the local area. They are of limited use as clearly they have not been developed by cyclists and mainly aimed at beach based tourists who want to go for an easy bike ride. This does not mean they aren’t useful if you’re passing by a tourist office but don’t expect too much.
I developed my own three day bikepacking route linking the high mountains areas with the beaches of Krk.
The routes in Platak are all included in the Bike Rijeka App. However there are two specific downhill mountain bike trails in Platak. To date there is no information on the webpage yet but presumably will be at some stage. One is a “flow” trail, a steepish gravel trail with hairpin bends but no technical obstacles. The other is a more technical trails with steep drops, roots and several jumps (avoidable). They are lift accessible at weekends in the summer but can also be accessed by riding up the main path to the left of the main lift looking up.
Bike Rijeka App
This is perhaps the most useful resource for routes as it provides a range of routes covering most of the mainland areas: Bike Rijeka App
Annoyingly there are several mistakes in both the routes and in the English translation. It does remain a useful source of information, I strongly recommend B7 Tuhobic Trail (main photo of this page) for a ride to the top of a mountain with amazing view. the app is however lacking information on how to get to the start of the routes, it assumes both use of a car and knowledge of the region. Where possible I’ve tried to provide access information.
There is a similar app for Krk Island, scroll down to find the link to the app. I haven’t used it so can’t comment. However it is very similar to the Bike Rijeka App and developed by the same company so I presume with the same pros and cons.
Take Adventure Website
Another good source of routes in the region and throughout Croatia and the Balkans. Take Adventure is an initiative by a keen and creative Croatian mountain biker. If you’re looking for more technical and single track trails this is a good place to look.
Gorski Kotar Bike
This is a week long route promoted through the mountains of Gorski Kotar, above Rijeka up the border with Slovenia. There is a website, and app. I find the route a little contrived and part is not even complete. However it has day trips on the same site which are worthwhile as are some of the sections even if I can’t recommend a holiday to do the whole thing.
I have developed my own bikepacking route: three days starting in the picturesque town of Kastav, through the mountains to Platak, dropping down the coast and along the east shore or Krk to Baska. Details are available here.