Translation:Amsterdam has a really big library!
Isn't "heel" a qualifier for "groot" in this sentence? Would "een heel grote bibliotheek" be ok? (I'd actually expect "een hele grote bibliotheek" to be wrong, but I won't be greedy now)
Got the audio and dismissed "hele", went for "gele" thinking Amsterdam is just the kind of place to have a big yellow library, but alas... :)
If only we had a big yellow library! That would be cool:p
There used to be a yellow submarine in a channel though...http://www.parool.nl/parool/nl/224/BINNENLAND/article/detail/3629321/2014/04/05/Kort-geding-over-onderzeeer-op-Bickersgracht.dhtml
Anyway; the fact that you thought 'een hele grote bibliotheek' was wrong, means that you understand the grammar very well. 'Heel' is a qualifying for an adjective, and normally that means it shouldn't be inflected. You just so happened to stumble upon the only exception to this rule! It is common in Dutch to use 'hele' before an adjective that also carries the -e inflection. (Basically you can treat 'heel' like a qualifier for the noun and not the adjective).
The good news is that 'heel' is also still correct.
a really big library > een heel grote bibliotheek / een hele grote bibliotheek
a enormously big library> een enorm grote bibliotheek
a really big house> een heel groot huis (NOT: een hele groot huis )