Hugest building by river is a bed and breakfast (10)
I believe the answer is:
guesthouse
'a bed and breakfast' is the definition.
I can't tell whether this defines the answer.
'hugest building by river' is the wordplay.
'building' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'river' becomes 'ouse' (Yorkshire river).
'hugest' with letters rearranged gives 'guesth'.
'guesth'+'ouse'='GUESTHOUSE'
'is' acts as a link.
Can you help me to learn more?
(Another definition for guesthouse that I've seen is " Boarding establishment".)