I've stumbled upon a few places where you can legally read free spanking stories, and my favorite has to be Literotica. It's a massive archive of user-submitted erotica, and they have a dedicated section for spanking content. The stories range from mild to wild, and the community is pretty active with comments and feedback. I love how you can filter by tags to find exactly what you're into—whether it's romantic, disciplinary, or just plain spicy.
Another gem is The Spanking Library, which focuses exclusively on this niche. The site’s been around for ages, and the stories are well-organized by themes and lengths. Some authors even serialized their works, so you can follow along like a proper book. The only downside is that the interface feels a bit dated, but the content quality makes up for it. If you're into classic erotica with a focus on spanking, this is a goldmine.