The Kjölur Route opens in early- to mid-June, and can remain open even into October. If you're driving, note that the only gas station (Jun-Sept 20) is at Hveravellir, 93km (58 miles) from Gullfoss.
From mid-July through August, Trex buses (tel. 587-6000; www.trex.is) connect Reykjavík and Akureyri via Kjölur daily in both directions, leaving Reykjavík at 12:30pm and Akureyri at 8:30am. SBA Norðurleið (tel. 550-0700; www.sba.is) covers the same route daily for more of the year -- mid-June through early September -- and buses leave at 8am from both Reykjavík and Akureyri. Both companies charge 8,600kr ($137/£69) one-way, and stop at Hveragerði, Selfoss, Geysir, Gullfoss, Hvítárnes, Kerlingarfjöll, Hveravellir, Svartábrú, and Varmahlíð, with short sightseeing breaks at Geysir, Gullfoss, and Hveravellir. The SBA bus takes 9 hours, while the Trex bus takes 10, adding a break at Kerlingarfjöll. The Kjölur Route is also included in two of SBA's bus package deals, the Highlights Passport (from 28,000kr/$448/£224) and Highland Circle Passport (25,100kr/$402/£201) -- both offered by SBA Norðurleið (tel. 550-0700; www.sba.is), an affiliate of Reykjavík Excursions.
The best information sources for Kjölur are the people or organizations who run accommodations along the route. The hiking organization Ferðafélag Íslands (tel. 568-2355; www.fi.is) operates five mountain huts around Kjölur and has the most regional expertise. The folks at Ásgarður (tel. 894-2132; www.kerlingarfjoll.is) know the Kerlingarfjöll area. Hveravallafélag (tel. 452-4200 or 894-1293; www.hveravellir.is) supervises Hveravellir and the website has printable maps of all hiking routes from there. Ample information on Kjölur's geology, flora, and fauna is found at www.ust.is, the website of the Environment and Food Agency of Iceland (click "Protected Areas," then "Hveravellir").
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.