This thread brings back happy memories of spotting as a teenager with some mates in the early/mid 70s. Most Saturdays were taken up with excursions. Some were ambitious far flung ones and/or railtours but we often followed an all day Saturday routine which went something like this.
Wimbledon or Earlsfield to Paddington either via the district line or via Waterloo and the Bakerloo. An hour or two at Paddington. I seem to recall quite a lot of toing and froing of engines from Ranelagh Bridge. Then Bakerloo and LMR electric to Willesden Junction. Down the lane to Willesden Shed. Ask at the front office nicely if we could have a look around. Usually got let in if we didn't make a nuisance of ourselves. I seem to recall seeing an LMS Gronk here in 72. Then over the hill to Old Oak Common depot. Walk in through the front gate and stroll down the hill to the turntable. Then a survey of the running shed, factory and more far flung sidings. No one batted an eyelid. In retrospect I am amazed how casual they were here at the time. On a warm Saturday summer afternoon there could be anything up to 20 or 30 spotty herbert interlopers distributed across the depot and sidings. A friend of mine was once walking along the middle of a track leading away from the depot to the mainline when a Brush 4 (or 47 as I believe young people call them) mooched gently up behind him and the driver sounded his horn to get him to vacate the track! Health 'n safety I don't think. Then we would walk along the back of the sidings towards the mainline and have our sarnies sitting on buffer stops watching expresses and freights whizz past.
Then LMR electric back to Euston - quickly copping the electric locos. There were as people have mentioned usually a couple of 25s and maybe a gronk in the parcels platforms (and how we took 25s for granted! -blub!). A bit dull for our tastes so then it was quickly along to Saint Pancras to cop Peaks and then the rest of the day at Kings Cross - 40s, Peaks, Deltics, Brush 4s, A1As etc. Brilliant. Then home. No mention of shed bunking being made to assorted parents etc.
Favourite London stabling point - Kings Cross Hands down. It had the combination of visibility, brilliant side views of engines doing the 'Kings Cross Shuffle' and classic traction.
I remember the first time we went to Kings Cross we had no idea about the lines from the underground system - imagine our bafflement when two LU battery locos pulled an engineering train out from the mysterious hole in the ground. What in the name of Sam Hill was that we thought. Happy days!