As with some others, my choice would be to go back to my teenage years, which being the early 1970s was certainly not a Golden Age for BR.
This prompted me to pull out old BR and Selnec timetables for 1970 to work out an itinerary based on my own interests, which include multiple flavours of sparks around Manchester and some long-gone local lines.
1. An early start from home* on a sunny summer's morning, equipped with modern DSLR, spare batteries and plenty of memory to record proceedings.
2. Spend an hour or two at Springs Branch. Photograph the varied and characterful rail traffic on the WCML back then (which is what got me interested in railways in the first place) with a background accompaniment of the ting-ting of block bells and crash of levers from the mechanical signalboxes.
3. Corporation bus to Wigan town centre for the 09:42 Wallgate to Bolton (ex-Liverpool Exchange train, probably a Cravens 105 DMU).
4. 10:02 Bolton to Bury Knowsley St. (Bolton - Rochdale train, probably formed by the DMU from Liverpool Ex. but not shown as such in the public timetable).
5. Walk to Bury Bolton Street for the 10:30 Bury to Manchester Vic (a Class 504 1200 V DC third rail EMU).
6. Walk from Victoria station to Cannon Street for the 11:11 Selnec no. 64 bus as far as Old Trafford (probably a Mancunian bus).
7. 11:34 Warwick Road to Oxford Road EMU (1500V DC Altrincham Electric).
8. 11:50 Oxford Road to Piccadilly (short hop on a 25kV Class 304 EMU heading for Alderley Edge via Styal).
9. 12:15 Piccadilly to Dinting (1500V DC Class 506 for Glossop/Hadfield).
10. 1½ hrs at Dinting watching Woodhead electric freight - hopefully still quite frequent back in 1970. If I'd set the Time Machine dial to summer 1969, I might have seen electrically-hauled Manchester/Sheffield expresses too).
11. 14:10 Dinting to Guide Bridge (another 1500V DC Class 506).
12. 14:38 Guide Bridge to Stalybridge (Stockport/Stalybridge Paytrain, which ran regularly through the day back then. Maybe a Gloucester RCW Class 100 DMU).
13. 15:04 Stalybridge to Leeds (Class 124 Transpennine DMU to Hull)
14. Connection from Leeds to York, arriving York at 16:44.
15. 3 hrs early evening at York observing ECML & Deltic action.
16. 19:39 York to Leeds, then 20:20 Leeds to Man Vic via Standedge (Peak or Class 40 plus Mk.1 stock).
17. 1 hr at Man Vic observing late evening preparations for the abundant parcels and newspaper traffic.
18. 22:30 Man Vic to Wigan Wallgate DMU, arriving 23:10, ten minutes too late for the last bus - so a nice walk home to finish.
* - Compared to the good old days, one thing I would do differently when issued with my Time Machine 24hr Day Rover ticket is get out of bed early!
As a typical teenager, I was never in a hurry to get up in the morning, compounded by no-one in our household being "morning" people.
As a result, I never left the house before 9am, meaning not arriving at local hotspots before 9.30 or 10.00, and I'd already missed all the day's morning peak action.