The Otago rail trail is 150 kilometers long and extends from Middlemarch to Clyde and can be easily fitted into your cycle touring ride. The surface of the trail is not perfect but can be negotiated on a touring bike provided you are not trying to cover the distance to quickly.
The Otago rail trail has become a very popular ride especially for those just taking up cycling. This is because it is off the road and as it is on an old railway the grades are not too steep and also because there are lots of cafes and accommodation along the way so that you can do shorter distances if you are not yet ready to do 80ks a day or want to take more time enjoying the countryside.