The Tutorial Is Too Hard튜토리얼이 너무 어렵다

Can anyone will tell me at what chapter does he goes to defend the dragon fortress where the lizardwoman died.

Not bad at all, and an interesting way to describe the descent into insanity by the MC and the way others view him. He is massively OP and people are terrified of the MC. They can tell something isn't right in his head, like quietly crazy.

For years he was stuck alone in a tower climbing plot, in hell difficulty which everyone dies at. The MC has been the only survivor of his difficulty since the beginning, while the other difficulties have groups and human contact. Once a year, all difficulties come together in the tower for a fair, and can use a tower forum, but no contact with the outside world.

As others said, the story is told in a series of flashbacks and then present time. Can be confusing to some, but I found it charming. I like the writing.

So you basically a novel about a solo hunter gaining traits and raising them - pain resistance, poison resistance, ect while climbing floors. Until it requires another hunter for both to kill their bosses and open that levels gate simultaneously, then a more abrupt descent into madness and despair. The MC eventually just decides to break the game and take revenge upon those who trapped him here.