Routes

[Bazzer]

Personally I tend to mix it up a little. If I want a fixed (ish) mileage, there are routes I know up to 70 miles which give me a choice of flat, rolling or lumpy. But those same routes also have lots of roads off to explore and as someone who has a non mapping garmin, for a non commuting ride, for me, very often part of the pleasure of being on my bike, is discovering out where you end up rather than knowing beforehand.
On the very odd occasion I have realised my wanderlust has been excessive and I needed guidance about how to get home directly, there is always google maps on my 'phone

 

[Ajax Bay]

when you set out for a leisure ride [alone] . . . do you always know where you’re planning to go?

Nearly always.
Weather: I'll invariably take the forecast weather into account - if there's a wind blowing I'll prefer to return with its assistance. If showers are forecast, this may influence where I go (can't go south from here, though).
Sunshine: If the forecast is 'sunny', then I design a ride which goes clockwise (talking 5 hours here). That way I haven't got the sun in my eyes, and nor have the motorists behind me.
Distance/Stops: Normally I plan my route on RidewithGPS so I have an idea of its distance and the cumulative distance of the various villages. These villages may also offer a shop and/or pub.
Roads: Prefer to stay off A roads (except where ‘bottlenecks’ force me onto them) but sometimes OK. B roads OK, but some can be busy - and you get to know those. Roads which used to be the main roads (eg the 'old A30', the old road which parallels the A361) are well worth using. At the other end of the highway scale I seek to avoid narrow roads – the one that are shown as narrow yellow on the OS 1:50,000 maps. Some of those lanes are lovely but many are of a width that means that you cannot be sure that you will be able to cycle past a car coming the other way: this increases the need for caution and thus reduces speed. And at this time of year, the wider minor roads (wide yellow on the OS 1:50,000 maps) are driven more and therefore less likely to be covered in leaves, hedge trimmings, mud and other farm detritus. They also tend to be better maintained IME. And you know that you'll always be able to get past a car coming towards you.
Cycle Paths: Where there is a decent off road route I may follow it but 'going' is important. For example: the Exe Estuary path (Dawlish Warren/Exeter/Exmouth), the Grand Western Canal towpath (Tiverton) and the canal through/NE of Taunton, the Tarka Trail (Barnstaple, Bideford and south towards Hatherleigh), the Camel Trail (Padstow/Wadebridge/Bodmin then up the R Camel valley), the Strawberry Line route from Axbridge (Somerset) to Yatton, the 'Two Tunnels Greenway' south out of Bath, the Bath>Bristol cyclepath, the Caledonian Canal towpaths NNE of Fort William to Fort Augustus.

 

[Racing roadkill]

My rides evolve as I ride. I only have a strict route if I've got a deadline to hit. That's very rarely the case.

 

[Dave 123]

Most of my rides from home head out south and west of Cambridge. My main priority is quiet roads, with scenery. As we all know Cambs is flat, but I can get a couple of decent hills in. I tend to know my route and stick to it (sometimes)

I will often knit different parts of different loops together and do them from the opposite direction. One day after doing the route the 'other' way I spied a bloody great windmill that had evaded me on the countless times I'd been in the opposite direction!

 

[Sea of vapours]

Invariably I know where I'm going to go since:
- The key factor is that I'm not a fan of mornings, meaning that I leave as late as I can commensurate with having 30 minutes or more of daylight at the end of the ride, so I need to know where I'm going so that I can reliably get back before dark as I'm also not keen on riding in the dark.
- There aren't an awful lot of roads around here (where 'round here' is about a 60km radius) and I generally do about 100km.
- They are all notably hilly and my average speed is significantly affected by exactly how steep those hills are. Up to 10% is not worth factoring in, but if the route has lots of 10-20% in it then that'll be slower both up and down and drag the elapsed time out a fair bit. I can't vary the route much without hitting an unplanned steep thing.
- I don't favour out and back routes, so shortening rides is generally not possible as I do loops in general and the hills tend to mean that there aren't any short cuts beyond a certain point, or if there are then they're not short in time terms as, again, they're probably over an unplanned steep thing.

The only deviation from the above is if I'm out to do some kind of intervals. In that case, I still know where I'm going since that needs particular roads (e.g. gently up hill for 15km) which severely limits which roads I use.

Having said all that, I don't generally plan where I'm going to go until the morning of the ride since I overlay what the weather is doing on what sort of ride I fancy doing and also choose routes based on wind direction, how cold it'll be high up, where there might be showers and, at this time of year, where there might be fallen leaves or all day ice on the higher minor roads.