It doesn't sound right. It could be: Mountaineering is attractive especially for young people beacase it is accompanied by hardship and adventure.

In the dictionary, were you looking up the word 'accompany' or 'mountaineering' :) Anyway, if your dictionary contained that exact sentence you should get another one - it's not correct. An example from my Collins dictionary: "Depression is almost always accompanied by insomnia" or you could say "Insomnia almost always accompanies depression". It means that they come together, at the same time.

There are some correct ways to put it right, like “ because it accompanies hardship and adventure". You may also uses other expressions, e.g. involves, or come with..., Hope this helps. Hui

Mountaineering is attractive especially for young people, because the hardship and adventure provided seems to be an exciting chalenge for them.

Say it like this: Mountaineering (or mountain climbing) is appealing to young people because it is identified with hardship and adventure.