Plant it to grow Dungeon Door. This works like a regular door, but it looks much more medieval.
Dungeon Door Seed price in Growtopia: sells for about 18/WL, buyers pay about 25/WL (median of 27 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: RKUYJ, PANSE, URRNO, I997, SONSON77