How do you feel when it takes a long time to read a book?

I have been reading The Historian by Elizabeth Kostova for about two weeks, now. Normally when it takes me longer than a few days to finish a book, it’s a symptom that I may just not be all that into it. But, it is not the case.

I absolutely ADORE The Historian. Kostova has obviously done a ton of research on the topic of Vlad the Impaler (aka Dracula).

The only problem is that it is taking me so long to read. Because it is so detail oriented, I am unable to read this while doing other things; listening to children, music,  or the TV, etc.  I need peace and quiet which only comes to me at night when every one is asleep. I, then, only get about 20 pages in before I have to submit to sleep.

Yesterday, I think I maybe read a page or two before I had to go to sleep because I was so exhausted by the day.

My Question to You:

What book have you read (in the past or present) that has taken you a considerable amount of time to read even though enjoyable?