Comic books may sound like something for kids, but don’t be fooled. Some of the most sought after collectibles in the world are comic books that once sold for as little as a dime. Take a look at the prices these comic books are bringing in and see if it would be worth it to take another look through your attic in the hope that you will find your own copy.

Action Comics #1 — First Appearance of Superman

The inaugural issue of Action Comics marked the first appearance of Superman and helped kick off the superhero genre. In 2014, a pristine issue of the 1938 comic, with its original price of 10 cents still on the cover, sold on eBay for $3.2 million, making it the most valuable comic book of all time. Action Comics No. 1 also holds the record for second-biggest comic book sale, with a copy previously owned by Nicholas Cage fetching $2.16 million in 2011. An estimated 50 to 100 copies of this first issue are still out there.

Amazing Fantasy #15 — First Appearance of Spider-Man

The staff of the Superhero Rating Department at Commonplace Fun Facts has unanimously declared that Spider-Man is the greatest superhero of all time. he not only has really cool powers, but he makes smart-aleck comments while beating up the bad guys. He made his debut appearance in issue No. 15 of Amazing Fantasy in 1962. A private collector paid $1.1 million for a copy in 2011.

Detective Comics #27 — First Appearance of Batman

One year after Superman’s first appearance, Detective Comics #27 introduced the world to Batman. In 2010, an anonymous buyer purchased a well-preserved copy of the 1939 comic for $1 million in an online bid. An estimated 100 to 200 copies have survived to the present day.

X-Men #1 — Debut of the X-Men

The best-selling comic book is Marvel’s X-Men. This team of mutant heroes was introduced in the 1963 issue X-Men #1, introducing the world to Cyclops, Beast, and Magneto. In 2012, a copy sold for $492,937 at auction.

Marvel Comics #1 — First Appearance of the Human Torch

Marvel Comics began as Timely Comics in 1939. In a foreshadow of what it would become, it launched a publication entitled Marvel Comics that same year. It would be almost another quarter of a century before we would see Spider-Man, the Hulk, or the X-Men, but Marvel Comics #1 did introduce the world to the Human Torch, albeit a decidedly different version than would appear as part of the Fantastic Four. A copy of Marvel Comics #1 sold in 2001 for $350,000.

Suspense Comics #3 — Most Valuable Non-Superhero Comic Book

The third issue of Suspense Comics—a short-lived horror/thriller title—became the most valuable non-superhero comic book ever when a copy sold for $173,275 in 2015. The provocative cover (featuring a bound young woman about to be slain by hooded figures wearing swastikas) meant that some vendors opted not to sell the issue when it first came out in 1944, and today surviving copies are scarce as a result.

All Star Comics #8 — First Appearance of Wonder Woman

Take a close look at the cover of All Star Comics #8 to find out why this 1941 issue is in such high demand. Still don’t know? It’s not your fault. You have to look beyond the cover to realize that this is the first appearance of Wonder Woman. A copy sold for $936,223 on eBay in 2017.