The Otago Central Rail Trail is a 151 km dirt road roughly following the route of a disused railway from Middlemarch, northwest of Dunedin, to Alexandra in Central Otago. The railway closed in 1990; once the infrastructure had been removed, the Department of Conservation bought the formation and the trail opened in 2000. 13,500 people rode it in the year to June 2016.
Rail trails are about leisure cycling; this one especially. It's very easy cycling with hardly any significant grades except for a short central section, the track surface is a well maintained dirt road with hardly any vehicles using it, it's not very long, and it passes through or near several towns or villages, most of which have accommodation and supplies; so you don't have to carry much. Riding the whole thing in one shot is not difficult in summer, say on a gravel or XC bike. The scenery is stunning all the way, from the dryland agri basin on the east side to the fractured, lunar-like scarps farther west. It's worth doing it just to look at stuff. Do it in summer, February or March if you can, to get long hot days and see the scenery at its best.
Before the rail trail was built, this part of Otago was among the least visitor-friendly parts of New Zealand, despite its proximity to touristy Queenstown, Arrowtown, and Wanaka; places like Ranfurly, Middlemarch and Omakau were declining backwater towns servicing an agricultural sector from the 1950s, with facilities to match. Middlemarch still is; it's a mostly deserted dump with unmodernised facilities and a single hotel with boguns on both sides of the bar. Most riders bypass it, taking a shuttle to/from Dunedin directly from the trailhead about 500m out of town (you can also ride to and from Dunedin without using main roads). If you do stay in Middlemarch, choose the campground. It's rubbish, but it's out of town. Take food with you, or eat at the excellent Kissing Gate, a cafe on the main road through town (Swansea Street).
If Middlemarch is evidence that some horses can't be made to drink, Ranfurly clearly recognised a thirst. The town grasped the opportunity the trail offered and turned itself into one of the most attractive stops. Buildings were tarted up, the place was bedecked with flowers and new business opened to service riders. Food's great and there's an excellent coffee shop tacked onto the grocery store. The campground is excellent and has a range of accomodation. Omakau, the only other sizeable place on the trail, has a decent hotel, campground, coffee shop and grocery store.
The trail finishes in Alexandra, formerly a dull agricultural service town where people driving to Queenstown stopped for gas, which has undergone a huge transformation in the last 15 years to become a destination in its own right. It's a particularly good place for a cycling holiday, with backcountry roads and lovely trail everywhere. Alex has passable coffee, great food, a supermarket, fruit stalls and various wine businesses. It also has the full range of accommodation including a gigantic campground connected to the town by the excellent river trail along the Manuherikia river.
There doesn't seem to be any advantage to riding the trail in any particular direction. Winds are changeable and when Dodo rode it anticlockwise - with a few diversions along the way - there was a headwind all the way north from Middlemarch to Wedderburn, and a headwind all the way southwest to Alex; followed by a headwind north to Clyde. Apart from wind, and I was just unlucky, it's easy riding in either direction - this trail is all about the scenery. The best sections are through the Ida Valley, and the final section from Chatto Creek down to Alex - that bit is gorgeous.
If you cycle a lot, and you don't live near Central Otago, you might wonder if such a technically and physically easy ride, which might only take you a day or two, is worth the expense of getting there with all your gear (several companies will hire you a bike to do the trail, but they're designed for... well, if you cycle a lot you probably don't want to ride one). Never fear though, because this trail is actually best when you think of it as linking up a lot of other places that are very interesting to visit on a bike. Dodo put together an epic that used the rail trail to get round the middle bit of Otago. This involved several side trips to classic old Central Otago villages, the Clutha Gorge Trail, and stunning connector rides to and from Dunedin.