This series is the latest gem I came across. It isn't the only one I came across, but I've decided to only present ones that have gone over 200 chapters without getting boring, which is a very small proportion of the web novel population, lol.
In this series, Earth's greatest bare-handed fighter, a master of qi and warfare unmatched on our planet, walks through a tunnel to an alternate version of Earth where magic exists and an ongoing war between monsters and humans is threatening to end humanoid civilization. Armed with his large variety of chuunibyou combat techniques (even he admits it), his iron-like body, and his inherent immunity to magic-based attacks, he cuts a swathe through monsters and evil cultists alike.
Generally speaking, this story is one where the protagonist constantly flips people's conceptions over on their heads while consistently pursuing his own personal sense of honor and style of life. In a world where magical power is everything, he is the opposite, the most powerful mortal in existence while also not having a drop of magical power. The first story begins a bit slowly, with him faking it a bit to get a grasp on how his new world works. However, it quickly accelerates after the initial 'adventures' with the temporary party he meets after his initial arrival.
It needs to be said that the protagonist is essentially a 'Goku' type of character combined with the archetype of the stoic and ruthless warrior monk. He is extremely harsh with his enemies and those who are hostile toward him, while being incredibly forgiving and easy on his friends and allies. He can also get along with a wide variety of types, including kind-hearted and clumsy catgirls and cold-hearted avengers. However, he is also very judgmental toward those who don't even make the effort to be better, and downright cold and brutal to those who don't understand honor or even simple straightforward social mores that are nearly universal.
Overall, the series is immensely fun to read, though the second story is only coming out slowly, so it will be some time before it is complete.