In marble halls as white as milk,
lined with a skin as soft as silk.
Within a fountain crystal-clear.
A golden apple doth appear.
No doors there are to this stronghold,
yet thieves break in and steal the gold.
Answer: Egg.
This riddle appears in the following downloadable PDF files:
Can you solve one of the most famous logic puzzle ever?
Memory Matching game for kids, adults and seniors.
Connect the matching tiles and pop them all.