Two buildings, one landmark (5,6)
I believe the answer is:
tower bridge
'landmark' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'two buildings one' is the wordplay.
I cannot quite see how this works, but
an anagram of 'two' is 'tow' which is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tower bridge that I've seen before include "London landmark" , "a fixture between two Thames boroughs" , "sight in the capital" , "river crossing" .)