Think of the noun, nostalgia, when you long for the good old days of the past.
The noun nostalgia was invented by a Swiss doctor in the late 1600s. He put together the Greek nostos "homecoming" and algos "pain, distress" as a literal translation of the German Heimweh "homesickness." Originally, it was a medical diagnosis for mercenary soldiers. Today, it describes a bittersweet longing for the past. Think of the dreamy way your grandpa tells stories of his childhood — he's got nostalgia.