One minute from the station gate to the trees. Tsuruma Park holds about seven hundred and fifty cherry trees, mostly Somei-yoshino, and Nagoya's tourism site puts the peak between the last days of March and the first of April. Tsurumai station, served by both the subway and the JR line, is a minute's walk away.
That proximity is not a detail about the park. It is what the park is.
Cherry blossom on a mountain or inside a castle is somewhere you decide to go: you check the forecast, book a day for it, and travel. This is somewhere you end up without having intended to.
People come out of the ticket gate on the way home from work, walk into the park because it happens to be there, and are still sitting on the grass an hour later without having planned any part of it. Nobody took a day off to do this, and nobody had to. The park does not ask anything of you in advance. Among the famous sites that is unusual, and it changes the rhythm of the crowd: the park fills steadily through the late afternoon rather than all at once at midday, and it does not really empty again until well after dark. A park that busy on a Sunday afternoon would be a different place entirely.
Where to stay
A day is rarely enough.
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