Thanks, that is very helpful. Just created a GPSies account, and already discovered a couple of promising routes around Eger. Did a quick scan of Strava too, but that seems to be almost exclusively on-road routes.
Some more digging by myself gave me this site, also quite interesting. Though not much around Eger, it triggers me to maybe ride a bit further round the country:
And bikemap.net delivers some result too, even though not sure if it is mostly just unpaved roads or proper MTB trails: