The feature is a very common one throughout New Zealand and can be seen nearby existing railway lines and also where there have been lines in the past. These bits of rail and the distinctive square cross sectioned posts that are usually in pairs, are usually painted white and have pyramid tops are a very good pointer to past railway corridors.
I spent a lot of time figuring out the exact pathway that the now closed Roxburgh line took. In a lot of sections there is no longer a raised "way" and the two features mentioned above were all that I could find. Very often the otherwise disappeared "way" became discernible, and also, very often, made sense.
The container is a dark brown, screw topped tablet bottle.