we are thinking of travelling on a TLK train, but read that you needed reservations. Where can you buy these tickets? Just at a station before you travel or do you need to purchase the day before?
There are reservations in 1st class and in certain 2nd class trains - but I'm not sure if there are actually any trains where reservation is actually compulsory. Even 1st class isn't reservation compulsory, just optional.
However, on Intercity you usually still need reservation.
Not usually, but always.
If you want the cheapest tickets go by InterRegio.
But be warned that the quality can be diabolical ;)