Looks like an Art Deco Block, but with extra friendship - you can use this to allow access to others. Just, y'know, keep it secret. Hidden Doors are only cool if they're secret.
Hidden Door price in Growtopia: sells for about 25/WL (median of 428 offers from community Discords, past 30 days). Live price chart and the latest buy and sell offers.
Recently sold at: NVA, PJUCX, RCYAD, ACK1, YOLLAN