Mine is being taken to London by my Mum and Gran and, just past Clapham, seeing what seemed like hundreds of railway lines with hundreds of trains and then getting that sensation of moving backwards when being passed by a faster train.

Taking the car sleeper from London to Inverness when I was a kid, think it went from Earls Court or Olympia.Also remember going on a school trip by train (1966) to the French alps which involved the ferry at Newhaven and then to Paris and I think crossing Paris by Metro Gare d'Nord to Gare d'Lyon.

Being allowed on the footplate of a Spam Can circa 1962 at Weymouth must of been about 5.
Also around the same time watching a freight train pass on the Portland branch, been in the blood ever since.

Jumping about 5 foot in the air when a Class 37 at full tilt blasted through Church Fenton station when I was a young boy in the 70s. That got me into the whole train thing..   

Cudders

I remember my parents walking with me over the footbridge in Kenley and stopping to wave at the drivers of the passing EPB's and 455's who always blew their horns and waved.

Not my very earliest, but always makes me laugh when I recall as a youngster being taken on the London Underground Circle Line.

I was totally intrigued that there was a real-life example of my OO gauge trainset that didn't go anywhere.

Dad, thinking it'd be funny, told me that he'd lost my ticket and that I'd therefore have to stay on the train, going round and round forever.

Wasn't he embarressed when I started crying, screaming and pleading to be let off  

Was with my Nan. She used to take us to see relatives in London on the train. I recall waiting at a platform late 70's and holding my ears as a HST screamed into the station. We then boarded and I remember being fascinated at how quick the country side rolled by the window. My Nan told me for years afterwards that I told everyone sat near us on the train that we were the fastest people in the world because we were on the fastest train in the world (by that stage of my life I had'nt heard of the Japanese bullit train!)

Diesel would be bits of New Street and Moor Street in Birmingham, and in sitting in the front right seat of the 1st gen DMUs watching the driver and view forwards (assuming we didn't get beaten to what were the most popular seats in the train, a point the later units missed!)

Steam was Hampton Loade, watching what I suspect was an Ivatt 2MT going tender first over the bridge by the car pack. I really must go back there some day, I realised recently I've not actually been there for 25 years and it's all changed a bit.

Walking over a footbridge near Teddington with my mother and baby sister who was in a pram. We looked down onto the tracks to see a very very dirty Q1 shunting. My sister who was a very crabby baby, chucked my favourite picture book out of the pram, it went through the wooden slats of the bridge and landed on the track.

My mother must have gone to the nearest shunting yard or signal box because one of the railwaymen got my book back. I have models of the Q1 in 00 and N and still have the picture book. 

I'm not sure which came first, both probably happened in the same summer. Its either a very vivid memory of watching a class 47 hauled oil train thundering over the Lytchett Bay bridge in Poole, or climbing all over the rusting hulks in Woodhams yard. The year was certainly 1981, its easily remembered because my sister handn't been born then and I had absconded from where we were hollidaying to go and watch trains passing the bridge and my parents reported me missing to the police...well, I was 3 That and I'm sure it was '81 that Woodhams stopped letting people into the yard because people were thieving everything they could. I'll say here and now, the only things we took away were photos

When we were young (early 70s) every summer my parents would buy a week rover ticket which allowed
travel all over the North West as far North as the Lake District and into North Wales.We would go somewhere different everyday.... usually DMUs.More often than not it would mean a change at Crewe where anything was likely to be seen.

Aged 3 or so, falling asleep in the evening to the sound of the Wolverton Works Jinty shunting wagons and carriages around the yard with much clanging of buffers. Little did I know then what effect it had on me

it would have to be Steamtown, Carnforth (sadly long gone as a museum)

i remember several visits both with my parents and with school
on the school visit there was a rather narrow, steep slope up to the car park and the coach driver managed to burn the clutch out trying to get up and we spent an extra 4 hours waiting for a replacement 

also on one visit you could have a cab ride on Flying Scotsman 

fond memories indeed

dave 

Being taken to London from Tilehurst around 1970 at the age of about 7.  I remember being on Platform 1 on Tilehurst station waiting for the stopping train and seeing an express go through on the far platform.  I'm not sure what it was really, but I imagine it was a 52 or a 47, very noisy and powerful.

Then a year or so later my next door neighbour (who had been a steam train driver) was given the task of taking a preserved steam engine down to Didcot.  My dad took me to Tilehurst station at 5am to watch it chuff by at speed.  That was impressive, all smoke and steam and smelling of coal, and a big whistle too as he went by.

Around the same time my neighbour also took me and my dad to the Reading Diesel Depot on Cow Lane to have a look round.  I recall they had a Class 24 on shed at the time and we walked from cab to cab through the engine.  This will be failthfully reproduced in miniature on my layout.

From then on most of my time was spent messing about around Tilehurst station or bunking it (ED: travelling on the train without having purchased a ticket) to Reading.  Trainspotting mostly, and occasionally getting in trouble with the Transport Police*.  The fascination lasted until I discovered girls several years later and now lives on in model form.  (ED: The trains, not the girls ).

* Apparently walking on the tracks where mainline trains run is frowned upon.  And should not be tried at home.

My favourite memory is from my trainspotting days at Reading when a very kind driver allowed me and a mate to climb up into the cab of his Western as the train was stopped on Platform 4.  I remember the oily smell, the heat and the noise.

As an evacuee I was wheeled in my pram up to the railway bridge at Verwood in Dorset on the line to Salisbury to watch the trains go by I don't actually remember this, I was only one at the time. Then EMU's from the back of our flat in Cheam (then in Surrey) our garden backed onto the station wall but if you looked right you could see them approach from Epsom, the only thing that woke me was when the early 4am steam hauled goods was late. Then the big treat going up to London via Clapham junction with all those wonderful steamers, by that time I was into 3 rail Hornby Dublo, hooked ever since!