Easy to assemble.  I don't do well with instructions,and it only took me 30 minutes to put together.  My cats "helped" me put it together and couldn't wait to check it out.  I did put cat nip all over the faux fur to attract them to it and alleviate any smells it had from being bagged and boxed up.  After reading lots of reviews, I decided to go with this one as I was looking for something that would accommodate two young adult cats.  It seemed that it was a good size for my 2 one year old cats, but unfortunately it's not...the tunnel is too small for them, so it is not used at all.  The two top beds are also small that neither of my cats will lay on it.  They both like the middle section and like laying on top of the enclosed section, but that is only big enough for one cat, so they battle each other for that particular spot.   Because of all this, right now both cats can not be on it at the same time.   It is sturdy.