I don't have access to the server, and I would need to get to know the structure of a website with 4,000,000 pages. This is what I will be working on. I need to look at the website as a whole, and all individual elements, and possibly come up with a plan on what would need to be changed. There is some sitemap tools, but from what I remember, they don't work very well with big sites. What would be the best way to do it these days? How to get the website structure, and all urls, also fairly fast? Thanks.
What's the purpose for doing this? What are you trying to achieve? A bit more information would help in possibly pointing you in the right direction.
Take a look at 'network graphs' (a sub-field of computer science) - very useful for visualizing large-scale networks. I'd suggest taking a look at Gephi as an easy starting point