Ask HN: Where would you sell an expensive painting (~1M)?

Auction, either Sotheby’s or Christie’s (https://www.artsy.net/article/artsy-editorial-why-sotheby-s-...).

Have not tried this myself (yet), but you could consign with Masterworks. It's a platform for "securitizing" art investments that's gaining traction. Best of Luck ;)

https://www.masterworks.io/consign-with-us