Don't you get it? The tomb is somewhere in the library. You said yourself it used to be a church.
8 seconds sound clip from the Indiana Jones and the Last Crusade movie soundboard.
You can hear this line at 00:28:03 in the Blu-ray version of the movie.
Quote context
[...]
- Dad sent me this diary for a reason. Until we find out why, I suggest we keep it to ourselves.
- That window seems to be the source of the Roman numerals.
- Dad wasn't looking for a book about the knight's tomb, he was looking for the tomb itself.
- Don't you get it? The tomb is somewhere in the library. You said yourself it used to be a church.
- Look. Three. Three. Seven. Seven. Ten. And ten.
- Now where's the ten? Look around for the ten.
- Three and seven. Seven and seven and ten.
- You don't disappoint, Dr. Jones. You're a great deal like your father.
[...]