I had yet to travel on any part of the WHR south of Rhyd Ddu, even though it's been reopened for a few years now, so to do so for the first time in the cab of one of the mighty NGG16's was an incredible privilege.
Our loco for the trip was 87.
I had previously travelled in the cab of Garratt 143 to Waunfawr when it was oil fired but being on board one of these giants running on coal was a new experience.
The crew certainly need a lot more room to work to feed that fire and I soon discovered that the best method for keeping out of the way of Steve's swinging shovel was to stand right in the doorway half in, half out, enjoying a fantastic forward view along the boiler in the process.
It had been wet all day in that corner of North Wales and - not unexpectedly - she was a little light-footed for much of the climb out of Dinas towards Tryfan Junction. The addition of sanding gear on these machines can only achieve so much it seems.
Although I had been told in advance I was surprised how rough the Garratts are to ride on for a large articulated machine, especially compared to a Double Fairlie on which I have also be fortunate enough to travel. At one point when the rear unit joined in a particularly enthusiastic bout of slipping you could feel the whole engine pogo-ing up and down beneath your feet.
As it was a special event there was an untypically intensive service on the line and we passed K1 heading north on a demonstration freight at Waunfawr.
One of my favourite parts of the journey was the sinuous section from Bryn Gloch to Plas y Nant where you could look out of the cab and see the front and rear of the engine bending this way and that.
At Rhyd Ddu we passed 138 heading north with the final train of the day in that direction and where we took water.
Carrying on south we were soon breasting the summit at Pitt's Head and the fireman, Steve, told me to keep a close eye on the gauge glass showing the water level in the boiler. It was quite remarkable to watch it drop at least an inch or so within a split second as 87 pointed her nose down the slope towards Beddgelert.
Naturally this was a very interesting part of the journey for me, my first chance to travel around the S bends above Beddgelert that we have spent so long studying and attempting to recreate in miniature.
Where the tracks come closest in the centre of the S the height differential is very apparent...
Cutting Mawr was immensely impressive..
And the big 180 degree bend on the embankment is too..
Until finally we rolled into Beddgelert station.
Looking through the cab window it is hard to believe that the Garratt is going to fit through Goat Tunnel.
The pass of Aberglaslyn is the most famous section of the WHR with good reason - it is a truly spectacular section of railway line - and travelling through the long tunnel on board 87 is an experience I will remember for a very long time, although I can only wonder what it must be like on the uphill climb.
On the Cross Town Link through the streets of Porthmadog my admiration of the crew rose even further.
I was struck all through the two hour journey how closely they have to work together to watch the line ahead. It's hard enough to see the road with the big fat boiler and water tank in they way on a straight stretch of line, but the bends are completely blind and they truly have to act as each other's eyes.
Nowhere was this more apparent that when we approached the first tramway section across Snowdon Street.
I spotted a gang of teenagers hanging around the crossing and sensed trouble.
Sure enough, as we steamed nearer the crossing they began playing 'chicken' running across the road in front of the locomotive. The line here is on a curve and as they played silly beggers they were momentarily completely out of view of both the driver and firemen, hidden by that great big water tank at the front.
I could feel the anxiety this must have caused our driver, Aled, at this moment. Steam engines, even narrow gauge ones, take a while to stop and there comes a point of no return where the driver is committed to taking his train over the crossing and is left to hope that some idiot kid doesn't choose to attempt one final dart in front of his engine.
No wonder he leaned out of the cab and gave them a piece of his mind as we passed.
After a pause to start the crossing lights we rolled across Britannia Bridge and onto The Cob and the connection with the FR.
It is a somewhat surreal moment as the NGG16 appears to drive down the Queen's Highway.
After being pulled back into the platform we were soon unhooked and charged light engine across The Cob to Boston Lodge Works. I don't mind admitting that the burst of acceleration after we cleared the last point had me rocking on my heels into the cab backsheet. Quite nippy these Garratts...
While I left the engine here and prepared to repair to the pub there was plenty of work left for the crew to put 87 to bed.
Steve had a hard job clearing out the fire which was an almost solid bed of clinker. It was a good job it was the last trip of the day because he reckoned there would have been no chance of making it up the hill if 87 had needed to take another train to Caernarfon.
Before wrapping up this rather lengthy post I must express my thanks to my driver Aled Lloyd and fireman Steve Holland for being such excellent company and allowing me to share their engine for a truly unforgettable trip.
Diolch yn fawr.
And heartfelt thanks too to Himself for arranging this wonderful surprise for me just days before my 40th birthday.