German town Seamus regularly visited (3)
I believe the answer is:
ems
'german town' is the definition.
(Bad Ems is a German town previously called Ems)
'seamus regularly visited' is the wordplay.
'regularly visited' means one should take alternating letters (letters are taken at regular intervals).
The alternating letters of 'seamus' are 'EMS'.
(Other definitions for ems that I've seen before include "Units of print measure" , "Measurement units in printing" , "Printers' measures" , "German city" , "German spa; print measures" .)