In the background of level 3, there is a vampire frozen in a block of ice. This vampire looks much like the titular character in the old German movie Nosferatu.

Much like the original Castlevania, there's a hidden Moai (the Easter Island head from Gradius) treasure. According to Ho-Ghan Liu's FAQ, it's at the beginning of level 4. Go up to the top of the tower, and just before exiting, walk right and fall and you'll find a Moai for 4000.

According to Doug Riggle, the large statue crying tears in level five is actually the Greek goddess Athena. The same statue can be found in the Parthenon in Greece. Doug sent this picture, a replica of this statue found in Nashville, Tennesee.

One for the "What the Hell?" file: hidden in Castlevania Chronicles, there's a picture of a super deformed Simon smoking a butt. It's hard to read, but according to cool person J. Soler, he says that it says "nise simon sanjou", which means something like "Here's Fake Simon!". You have to play the game through several times, and after the eighth run through or so, you'll see this picture in the mirror at the end of level six.

Castlevania Games - Akumajo Dracula X68k - ADX68k Weirdness