All that remained were two lounge chairs beside the pool ?
All that remained were two lounge chairs beside the pool, which hadn’t changed since the day it was dug and plastered in 1974.

I would like to know what does "which" refer to ? the pool ? or the lounge chairs ? Thanks.

Question

All that remained were two lounge chairs beside the pool ?
All that remained were two lounge chairs beside the pool, which hadn’t changed since the day it was dug and plastered in 1974.

I would like to know what does "which" refer to ? the pool ? or the lounge chairs ? Thanks.

Answer

Think about this, Kelly. There are two obvious clues here. 
One is grammatical, and the other is plain common sense.

Can the pronoun 'it' refer to two chairs?  No.
Can the process of digging and plastering refer to two chairs?  No.