Sehnsucht (German) is the longing or yearning for something unachievable by someone, be it love or some of the motives common in the romanticism like travel and freedom.
Nostalgia for an event or thing that you have never experienced or had before.
Person A: Hey... I just got this old-fashioned TV the other day... Even if I never had one, I still feel nostalgia for it.
Person B: That's called Sehnsucht.