My first English book was Journey to the Center of the Earth 😀
Well, it depends on the level. Reading a book can be quite tricky because of the description you can find. Dialogues can be easy to understand, actions probably as well but not always. Descriptions have a lot of vocabularies that you might not familiar of.
Personally, the best ones are screenplays because it's like reading a movie and you can find plenty of them on amazon or in general online. They are great for beginner and intermediate, but of course they offer less to advanced learners who want to learn less common words.
In general, if you want to read a book that is not about a story, non-fiction are the way to go. They give you a lot of useful words, grammar and they teach you something.
All books are difficult in a way or another, and every type offers something different. So it's up to you.
Thanks Davi, I haven't read this one but I think that Verne writes well and uses simple language (I've read Around the World in Eighty Days). But, as you mentioned, the vocabulary can be a challenge unless translation is in modern language.