So many good questions. I have probably asked all of them myself a dozen times. The tunnel and stuff question. If aliens have advance technologies, like interestellar, thousands of years ahead of us, just the excavation material could likely be refined or molded into products. We have 3d printers today, but could any material be reconstituted into a matrix to make things? If your boring equipment was so advanced in solidfied the very walls into concrete, or they carve into solid rock... We have seen versions of that. The city Petra? I suspect something like Elon Musk's boring company has been around longer than he has held it.

Human, or human like aliens.That is definitely a problems if we are only allowed one model of existence. Humans originated on earth model. This doesn't mean no evolution, I believe evolution is solid enough. If there has been interstellar travel for millions of billions of years, it is likely that the Milky way is well mapped out, and everything habbitble is taken, and anything that can be transformed is habbitable. And if there is a pecking order, and life is being distributed, then all known species are catologued and re-utilized to meet environmental niches they're best adapted to. If the greys have been breeding us, and they travel the galaxy, there could be pockets humanity elsewhere. If humans are indeed a valuable product, why leave it to one planet? Maybe all the races came from one human, the way all breeds of dogs came from one wolf, or maybe all the races on earth are independent alien colonists- still all human, but all of us had missions to come here for a task, stewards of a planet. I really don't like the Earth is a prison story, but if Earth is Australia, there is that story, too.

I owned a copy of that book. I didn't mention it by name. I think there are several similar. I am baffaled as to how we have such a full encyclopedia of aliens. How much of it is fiction? How much of it is lore? Every culture has something- the Jinn, faeries, the little people, the ant people, sprites... Even Big Foot fits this pattern of mythical, egional creatures that have a purpose of reminding us we're not alone. Maybe man can't fully grasp God, but angels and demons are solid enough in our heads.

keep asking questions! Exhaust all your usual explanations, then go beyond fancifal to the radical alien. Souls are multidemensional beings. Every planet in the universe is a product or project of soul, with missions and plans that last billions of years. We develope life from scract, through soul intention and interaction with the very particles of reality, and then occupy the life forms when the vehicles have evolved sufficiently sophisticated mechanisms to hold our essence? (That idea resonated with me from Journey of Souls, Michael Newton.)