I almost always book such trips well in advance, to take advantage of cheaper tickets in GB / on Eurostar, and then use either the Rail Europe or individual country rail service websites for onward travel, generally from Paris. I haven't yet had occasion to checkout what difference, if any, the merger of Eurostar & Thalys has made to mainland Europe ticketing options.

One rather jolly exception to this, some years ago, was DIG>PLY with GWR, a pleasant early evening stroll to Millbay Docks, Brittany Ferries to Roscoff, and then SNCF to Brest, changing at Morlaix, to join a friend's yacht for a lovely sailing trip as far as Morbihan and then back to Dartmouth. I am pretty certain that absolutely no through ticketing options existed at the time.

 
Does Heathrow Express from Paddington to Heathrow count? 

 
I claim Severn Tunnel Junction to Filton Abbey Wood. 

 
Several return trips either Falmouth or Penzance to Wick in days gone by (via Paddington).

 

Tribute was a ticketing issuing system to which you could attach various printers including the ATB for Eurostar & continental tickets, but it was also the standard system for various TOCs for issuing domestic tickets.
After we ditched continental bookings and the ATB, we carried on using Tribute until it got replaced by Star. This happened after Wessex Trains disappeared as its successor, FGW, replaced it with Fujistu's STAR system.

** ATB = Automated Ticket Boarding or Automated Ticket & Boarding Pass.    I was never sure which!

 
Remember "Persil Tickets" ?  A promotion from the 1980s that gave 2 for 1 travel (IIRC) and included Amsterdam and a couple of other overseas destinations in addition to domestic travel.

 

That's a British "slightly", right?   . I suppose the clue in the question was the reference to "Great Britain" in one of the potential answers.

I could add Melksham to Swansea loads of times ... and there are those who consider you're in a different last west of St Budeaux.

 
Admittedly a little tenuous for "taking an international trip from my local station" but I've started and finished one time at Redland in order to get to and back from Birmingham Airport and once to connect with the Bristol airport bus at Bristol Temple Meads.
Before living where I do now, my most accessible local station was Temple Meads an I used that to reach a number of different ferry ports.

Edit to add:. Went from Temple Meads to London and on to Brussels by Eurostar.  This was before my local Redland Station had a useable enough service to be able to start and finish from there.

 
Pinhoe to Strasburg and Kandersteg to Pinhoe back in September 2022 as part of a GreatRail package (other rail holiday operators are available).

And, stretching the 'international' ever so slightly........... Pinhoe to Fort William and back several times.

 

The 'Citalian Express', which ceased to run almost within living memory and might be covered by your 'CIV' quiz item or perhaps it wouldn't be. Anyway, local station to Victoria, then Folkestone Harbour, boat, then a through train from Boulogne's Gare Maritime to various destinations in Italy.

http://www.eastbank.org.uk/citalia.htm

Mark

 

Was that the one that was known as 'Tribute'?  I remember them - great big things and very slow (compared with APTIS) and they didn't last long!

 
Many stations used to issue european tickets back in the day, usually the ones with a Travel Centre.
 One big stumbling block came along when SNCF (French Railways) barred the use of hand-written tickets, which was the standard way of issuing continental rail tickets in this country.
Some stations did carry on for a while, including us at Truro, as we had an ATB (the BIG ticket) printer installed for issuing Eurostar tickets but even we stopped in 1999. It just took too long for very little return and, like most places, we had fewer staff than before.

 
Can we have a "can't remember" button? As in I can't remember whether Bristol to Waterloo (it was that long ago) was on the same ticket as the Eurostar and onward DB trains? I suspect it was a separate ticket, though I have a feeling Waterloo to Cologne was all one ticket. In any case, I'm not sure whether you're counting journeys with a series of separate tickets? I could also ask if you're counting journeys were "home" was not the UK, but that would probably just complicate matters even if my answer would be simpler!

 
AIUI the international tickets at Bath Spa was down to one enthusiastic member of staff there. So I was told at the time. So closed when he retired.

 
Always think it's funny* that Bath Spa had an international tickets desk - that closed at about the time that Eurostar first ran, the dream of through trains from other than London was still in the air, and the rolling stock for through sleeper trains was in production. Years later, it was difficult to find a scan of the artwork for a channel tunnel promotional tea cloth from the days of construction of the tunnel.

Mark

*Not funny.

 
I ticked 'Something else'.

By coach From Taunton bus station to Busáras Dublin via a change in Birmingham, then ferry from Holyhead.

 
I travelled Melksham to Thun on the day after we got a decent service back in 2013 ... and I have travelled to Limerick, to Dresden, to Catania, to Nurnberg, New York and Ljubljana.  Many but not all have been good, green, overland issues but I can't go down to my local station and buy a Melksham to Milan ticket from the ticket machine, or from the staff in the station caf - nor can I simply ask for one on the GWR website.  It's more complicated than that, to the extend that (I believe) it puts off many a traveller who would use a straightforward facility.

I have listed some of the options that are (or were) available above - which have you used?   Please add those  have overlooked as "something else" and comment to let me know what they are.