I noticed this sign at JR Okachimachi station exit when I went to buy supplements the other day.
I asked what it is a station staff, but he has no idea whatsoever. "I don't know about it at all. When this is set up there? "
でも見るからに線路沿い・高架下な感じなので探しに行くと…
But it seemed that there must be something near there, so I started look for in its neighborhood, then...
ありました! 高架下が綺麗にお化粧されて、小さな街ができています。
found it! An under the JR track was cleaned up and get painted with white to become a small town.
2k540 AKI-OKA ARTIZANという名前だそうです。
最初の5ケタの読みは「ニーケーゴーヨンマル」、意味は「鉄道用語では東京駅を起点とした距離『キロ程』で場所を示します。当該施設は2k540m付近にあるため『2k540』とし」ているそうです(公式HPより)。
The first five digits is read "knee-kei-go-yon-maru," it means that to indicate a place it's always start from Tokyo Station by railway technical terminology. And this place is located around 2km and 540m from there. That's why (from official website).
They will be open at 13:00 on this Friday.