I registered to ask for some help identifying a book. It was likely the very first space opera / science fiction novel I read, but I was a pre-teen/early teen exploring my older siblings' bookshelves so I have no memory about its name. I was 8-10, so it must have been older than 1996-98.
It was full of suspense and entire passages where I was trembling with fear. While I remember very little about the plot and the setting, I vividly recall my feelings and images while reading the about the first encounter with these strangest sentient beings.
The main characters of the novel were exploring a strange world of very vast emptiness between massive, miles-wide and complex fortresses/space-bases - one of which they try to infiltrate.
The villain aliens are very tall transparent perfect cylindrical column-like beings emitting some light; some parts of their insides can also be seen (the equivalent of a "heart") and maybe reflected the mood of these beings.
There were different types of aliens. Either they were the same species and not uniform or there were different "classes" - some were just servants (and may have been more "solid", silver-like orbs) whereas the most important rulers were more gaseous. Either way they were an advanced civilization and had to be infiltrated and defeated.
I wish I could find this novel again... I tried Googling the species but found nothing.
Any idea what this might have been, and what its name was?
UPDATES: Thanks for everyone's comments and answers so far. Appreciate that you looked into it... but none of them are the one I meant :( I never imagined this was such an obscure and unknown book!
There are many similarities with the books/novels you pointed out, but I am quite sure of one feature: it was space opera/futuristic science fiction and potentially also involved some space travel by the main characters. I vaguely remember some elements of a "Hobbits in Mordor" style ending, i.e. the main characters are a small party traveling to this world/planet and need to explore and infiltrate the world to destroy the extremely more technologically advanced enemy (If I correctly recall, they ultimately do).