A nice place to lay up, thanks (5)
I believe the answer is:
yalta
'a nice place' is the definition.
The definition suggests a singular noun which matches the answer.
'lay up thanks' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'thanks' becomes 'ta' (UK informal version of 'thank you').
'lay' back-to-front is 'yal'.
'yal'+'ta'='YALTA'
'to' is the link.
Can you help me to learn more?
(Other definitions for yalta that I've seen before include "Black Sea port" , "Crimean resort and seaport" , "Black Sea resort" , "wartime meeting-place" , "Crimean town famous for WW2 conference" .)