Els - After doing Trans-Siberian railway a while ago I wouldn't repeat it. WHS-wise (and more interesting) would be to go to Vladimir/Yaroslavl than to spend 50 hours on the train. And then go to Irkutsk by plane.
I do understand, but I also try to avoid the hit-and-run ticking of WHS without seeing anything of the country.
To share my Bolgar and Sviyazhsk plans A, B, C en D, for future use of others:Getting to Bolgar and Sviyazhsk
For Bolgar I have:
a. River Ferry named 'Meteor', leaving at 8 am (2h24min), returning the same day. Yandex schedule
has the times and dates til when they run (easy to use with the Google translate function). Tickets can only be bought at the port.
b. Bus from Southern Bus Station, leaving at 8.30 (3h40min), also returning the same day. Also on Yandex schedule and best bought beforehand in person.
c. Shared taxi from Kazan MegaMall at 11 am, as per information of Michael Novins (I do have the driver's phone number)
d. Bus Tour with a Russian tour group - Barabanov shared with me the details of http://www.tatturist.ru/
, who have tours running on my dates (Russian only). Similarly, the tourist desk at hotel Tartarstan has been recommended, running daily bus tours in Russian to various sites around Kazan.
(e. Renting a car would also be a possibility, but I believe you need an international driving license which adds to the cost - during the shoulder season of mid-September one of the 4 options above should work)
For Sviyazhsk I have:
a. Take a taxi and make it wait for an hour or 2. Because of the relatively short distance (60km) this should not be a problem. Advertised on TaxiKazan
b. River Ferry, leaving at 9 am (2h10min), returning the same day. Same conditions apply as with Bolgar regarding schedules and tickets.
(c. there's a train as well, but the railway station is so far from the site you'll need another taxi (if you can find one))
(d. and there are day tours in Russian as well, see option d at Bolgar)