So: that's the end of my Attic Explorations -- for this trip, at least.  There's lots of things I didn't manage to do, largely because of the bad weather earlier in the spring: Pendeli is a wonderful mountain for cycling, and the north-west corner of Attica, up towards Megara, is also great (though exhausting).  Next time!

In case it's of any help to anyone thinking about a Greek cycling trip, I thought I'd jot down a few practical things here.

Athens Airport

 The airport is (probably accidentally; but never mind!) pretty bike friendly. 

Arriving: bikes tend to just come out on the usual luggage belt (there's no 'outsize luggage' delivery point).  For bike reassembly, I usually exit the terminal building and cross the road directly outside; there's a broad and quiet patch of pavement here with plenty of space to work, sheltered from sun/rain by a raised walkway, and with handy bins for any superfluous packing materials.  From there, there's a lift up to the walkway to the metro/train station. 

Departing: on the departures level, outside the terminal, there's again a big, sheltered space which is good for bike disassembly.  Bikes have to go to the outsize luggage scan, which (in my experience) is run very efficiently.  I've never been asked any questions about extra stuff in a bike bag, or my tyre pressure, or anything similar.

Bikes on Public Transport

All the metro lines take bicycles (with no time restrictions, and no need for a special ticket).  Bikes should go in the end carriage (and at the end of the end carriage).  There's no dedicated space, but the idea is that you won't get in anyone's way there.  In theory, there's a limit of two bikes per train, but I've never seen that enforced.  (In practice, the limit is imposed by whether there's physically space to fit a bike in: at busy times, it might be necessary to wait for the next train.)  All the stations on the red/blue lines have lifts, which are big enough for (at least) one loaded bike; not all green line stations have lifts, but they usually have bike-pushing-channels on the stairs.

All the Suburban Railway trains also take bicycles -- again, with no restrictions/ticket.  There's no special bike space, so just head for the quietest bit of the train and put the bike in doorway (and be prepared to stay near your bike, to move it to the non-platform side at stations).  In theory there's a three-bike-per-train limit, but again I've never seen it enforced.

Intercity trains (e.g. to Thessaloniki or Kalambaka) take bikes as registered luggage, for a five euro fee.  No need to book a space: take your bike to the luggage office at Athens station (there are good signs pointing the way), and pick it up either from the guard's van or the luggage office at your destination (depending on where you're heading).

Local buses and trams don't take (non-folding) bikes. KTEL buses (long-distance) take bikes at the discretion of the driver (i.e. if there's space in the luggage compartment, and if the driver isn't in a grumpy mood.  I confess I've never tried it!)

Bikes on Boats

All car ferries take bikes, usually at no cost: buy a standard foot-passenger ticket, but then board with the cars/motorbikes.  Someone will tell you where to stash the bicycle, and there's usually a bit of rope to tie it in place for the voyage.

Flying Dolphins in the Saronic Gulf tend not to take bicycles, or at least not officially (that is: if it's a quiet day, and the crew are in a good mood, they might let you take one on as luggage; but it would be a risk to rely on it, I think).  (Some of the longer distance high-speed boats do take bikes, though: there's a useful summary here.)

Mapping

Open Street Map/Open Cycle Map is pretty reliable, in terms of reflecting what is on the ground.  Its categorisation of the quality of roads/paths, though, is much more hit and miss.  If you're using a route planner which is based on OSM (e.g. komoot or cycle.travel) and have it set to 'unpaved', then you might find yourself on singletrack from time to time; if you have it set to 'paved' then you might regularly find yourself on unpaved farm roads -- these are often absolutely fine, but sometimes get a bit rough or (after rain) very muddy.  Online route planners will also often avoid theoretically 'main' roads which in fact are almost traffic-free. In other words, it's often worth double-checking an automatically-planned route.

For printed maps: Anavasi is the most reliable, and has fairly good coverage at a range of scales.

Greek Drivers

I know that Greek driving doesn't have the best reputation (even among Greeks!), but in my experience Greek drivers are -- from a cyclists' perspective, anyway -- really great, particularly at leaving plenty of space when passing (this is true even in central Athens).  Traffic levels outside cities are generally low, and drivers are usually patient when they can't pass safely.  Be prepared for a certain level of capricious driving: sudden stops, u-turns, reversing down a slip-road, etc.  But the corollary of that is that you can also expect quite a lot of tolerance for not-entirely-legal behaviour on your part, if that's ever necessary (e.g. a quick scoot the wrong way down a one-way street...)

Dogs

In my book, the only (slightly) bad thing about cycling in Greece.  The issue is generally with sheepdogs, rather than domestic or (other) guard dogs.  In Attica, they aren't too much of a problem, because there aren't that many sheep, and those that there are usually have a shepherd fairly nearby.  But they can still be an annoyance.  The strategy I've developed, which has worked so far (touch wood...) is not to try to outpace them (because they'll chase, and they'll win), but not to stop either (because what they're trying to do is to get you out of their turf): keeping going, at a steady pace, seems to be the way to get them to calm down.  But it's definitely a way to get the heart pumping...