mongols were still expanding westward until they hit the carpathians and caucuses, and even sent some expeditionary scouting parties through and found there wasn't enough grass to sustain their horses and the land was too poor and backwards to bother with. One of their scouting parties nearly defeated a European army on its own and the Europeans thought they beat the Mongols for good but it was just a small detatchment

https://en.wikipedia.org/wiki/Battle_of_Samara_Bend

They made it as far west as Bulgaria and the Carpathian mountains, and could have easily continued had it been worth it and had there not been annoying choke-points and bottlenecks and rugged terrain - eventually the Mongols did take Bulgaria, but as I was saying, the mountainous terrain in this region is really what walled them off and led to them being ambushed and defeated at higher rates, and reduced the effectiveness and mobility of their armies.