Bus tours are popular and convenient, but many visitors prefer the flexibility of a rental car. The cost of a single Golden Circle bus ticket is only slightly less than renting a cheap car for 1 day, and the stop at Þingvellir, for instance, is never long enough for a hike into the valley. With a car you might also work in Hveragerði or the Þjórsárdalur valley. The roads are open all year but can be very slippery and dangerous in winter. Note: If you plan on taking the interior Kjölur Route to Akureyri, you can see Geysir and Gullfoss then.
By car, Þingvellir is less than an hour from Reykjavík; take Route 1 north of Mosfellsbær, then turn right on Route 36. From Þingvellir, continue east on Route 36, turn left on Route 365, and turn left again on Route 37 in Laugarvatn; when Route 37 ends, turn left on Route 35. From there it's a short way to Geysir, and another 10 minutes to Gullfoss.
Regular service from Reykjavík Excursions (tel. 562-1011; www.re.is) costs a bit less than a formal tour and is an economical way to spend all day at Þingvellir. Bus 6 leaves from BSÍ terminal in Reykjavík daily mid-June through August at 8:30am, stopping at Þingvellir (9:15am-10:15am), Laugarvatn (10:45am), Geysir (11:15am-1pm), and Gullfoss (1:15-2pm). Bus 6a does the reverse route without extended stops, arriving back at Reykjavík at 4:45pm. A one-way ticket to/from Þingvellir costs 1,000kr ($16/£8); to/from Geysir 2,300kr ($37/£18); to/from Gullfoss 2,550kr ($41/£20). Children ages 4 to 11 get 50% off.
Bus 2 on Þingvallaleið (tel. 511-2600; www.bustravel.is) leaving Reykjavík's BSÍ terminal daily at 12:30pm from June through August, stops at Hveragerði, Selfoss, Laugarvatn, Geysir, and Gullfoss -- and on the return trip, Reykholt, Laugarás, Selfoss, and Hveragerði -- but does not allow time for sightseeing.
Bus 2 leaves BSÍ terminal at 12:30pm daily June through August, reaching Gullfoss at 3:15pm and Geysir at 4:25pm.
Organized bus tours leave from Reykjavík's BSÍ terminal, and prices include free hotel pickup and dropoff. Standard tours generally last 8 hours and leave at 8:30 or 9am. Reykjavík Excursions (tel. 562-1011; www.re.is) charges 7,000kr ($112/£56) for the standard Golden Circle tour, which includes Kerið Crater and Hveragerði. For Gullfoss and Geysir only, the "Gullfoss Geysir Direct" tour costs 5,700kr ($91/£46) and lasts 5 1/2 hours. Children ages 12 to 15 get 50% off; ages 11 and under ride free. The Golden Circle tour from Iceland Excursions (tel. 540-1313; www.icelandexcursions.is) costs 6,600kr ($106/£53) and includes Nesjavellir geothermal power plant, Skálholt, Kerið Crater, and Hveragerði. "Gullfoss & Geysir Express" costs 5,200kr ($83/£42) and lasts 6 hours. For the more culturally inclined, the 5-hour "Wonders of Þingvellir" tour, focusing exclusively on Þingvellir and the Halldór Laxness Museum, costs 4,800kr ($77/£38), with departures June to August 20 weekdays at 1pm. Ages 13 to 17 get 50% off; ages 11 and under ride free. Iceland Total (tel. 585-4300; www.icelandtotal.is) has a Golden Circle tour focusing exclusively on the big three destinations for 6,813kr ($109/£55).
Þingvellir has two visitor centers (www.thingvellir.is). Approaching from Reykjavík, the first you come to is the interpretive center, at the top of the Almannagjá fault; the turnoff from Route 36 is marked "Fræðslumiðstöð" (June-Aug daily 9am-7pm; Apr-May and Sept-Oct daily 9am-5pm; Nov-Mar Sat-Sun 9am-5pm). The center has fun and informative video displays explaining the area's natural and cultural history. Farther along Route 36 is the information center (tel. 482-2660; May-Sept daily 8:30am-8pm; the cafe is also open Apr and Oct 8:30am-8pm and Nov-Mar Sat-Sun 9am-5pm) with cafe and bookshop. The plan is to expand services at the interpretive center; so, by the time you are reading this, you may be able to find maps or park rangers there. Many visitors skip the information center anyway, since from the interpretive center it's a short and agreeable approach on foot down to the historical sites.
The Geysir Center (tel. 480-6800; www.geysircenter.com; June-Aug daily 9am-10pm, May and Sept daily 9am-8pm, Oct and Apr daily 10am-4pm), across the street from the geothermal area, has an information desk, cafe, and extensive souvenir shop.
The unstaffed Gullfoss visitor center (Mon-Fri 9am-6pm; Sat-Sun 9-7pm) is right next to a cafe and gift shop (tel. 486-6500; Oct-Apr daily 8am-6pm; May-Sept 8am to as late as 10pm), where questions can be directed.