Come out, come out, wherever you are!
1. In the closet
For your cat, your closet is a wonderful hiding place: it's dark, it's full of soft, fluffy things (is that a freshly washed towel?!), it smells like you, and your cat can climb up high, for safety.
Don't be surprised if Felix gets all the way to the top and evicts some of your clothes to make a good snuggle spot.
2. Behind the chest of drawers
If your cat doesn't like heights, it is possible that they have wriggled into that small space between the dresser and the wall.
However, this isn't a good or safe place for your cats to hide, as, depending where they have sequestered themselves, they may get hurt when you unknowingly open a drawer. Feline behavior experts recommend putting a bit of citrus or peppermint oil around the drawers to keep your cats away.