Sometimes you'll meet monsters which are too powerful for your level. In this case you can continue running your head against the wall trying to defeat them immediately or you can go elsewhere and return later when you're more experienced and better equipped (if you don't forget it
).
Corak's notes about the cave should give you an impression about what's in the cave, there's only one Cyclops King but many Cyclopes. Just wait until you have the joy of fighting three of them at once
.
There's an "Identify Monster" spell in the game.