Question

Nothing beside remain round the decay nothing that colossal wreck boundless and bare
What does that colossal wreck refer to

Answer 1

The idea conveyed here is that nothing is permanent. Everything will come to an end with the passage of time. The 'colossal wreck' refers to the trunkless statue of the king Ozymandias. The dilapidated statue is the only thing in this barren, lonely desert. The idea is that at some point of time, there might have been a temple etc but now nothing 'beside' remains.