My guide Sandra Mark parks the jeep in front of a snow-covered forest and pulls out a black shiny flint-shaped object from her bag.
"Right," she says. "We've got dragon glass. Are you ready for White Walkers?"
On a Game Of Thrones tour in northern Iceland, in search of locations where the hit HBO fantasy series is filmed, such jokes are inevitable.
In author George R.R. Martin's Westeros, dragon glass is the material that kills yeti-zombies stalking the north. The "glass" in question is obsidian - a naturally occurring volcanic glass you can find in Iceland.
We crunch down a snowy path, bare silver birch trees on either side. Eventually, we come to the edge of a vast lake.
Lake Myvatn (say "mee-vat"), the country's fourth largest natural lake, has a surface area of 37 sq km and is surrounded by a conservation area spanning 440,000ha.
It is here that a scene was shot of the wildlings, or free folk of the show's legion of characters, setting up their camp.
In summer, the lake teems with midges - hence its name, "midge lake", in Icelandic. In winter, however, only ducks such as black scoters and Barrow's goldeneyes disturb its clear surface.
The silence is slightly unnerving. Lava rock formations or islands dot the water. Legend has it that these used to be trolls, who had gone fishing on the lake at night, then turned to stone when the sun came up.
Sandra points across the lake at a row of stacked rocks, with an opening in the middle. "That's the entrance of the love cave that Ygritte and Jon Snow go into," she says, referring to a romantic scene in Season 3 between a wildling archer and the illegitimate son of the noble House Stark. "But the cave is somewhere else."
Satisfied, we trek back to the car. A rustling comes from the direction of some bare birches and Sandra mock-hisses: "White Walkers!"
But it turns out to be just a couple of other tourists. We grin sheepishly at them.
The Game Of Thrones-themed tour by The Traveling Viking (www.ttv.is) is just one of a number offered around Iceland. Sandra says theirs started in 2012, after the tour company's boss Jon Thor Benediktsson wrote to HBO with the idea.
"We thought we wouldn't get a response because we're a small company," says Sandra. "But, to our surprise, they replied really quickly."
When the show's producers returned to Iceland to film again, they went on the tour too.
The seven-hour tour, which costs 22,000 Icelandic kroners (S$221), starts from the northern Icelandic town of Akureyri, spans the Myvatn area and includes entry fee to the geothermal Myvatn Nature Baths - a splendid freshwater lagoon similar to Iceland's famed Blue Lagoon, but sans white silica-rich mud and crowds.
Sandra picks me up at 9am from my hotel in town in a jeep with giant wheels. I have to take a running leap to vault into the passenger seat. We are joined by her colleague Solveig Bennyjar-Haraldsdottir, who will soon take over as guide for the tour, as well as Emily Moore, a backpacker from New Jersey.
As we drive out of town, towards dazzling white mountains and along the long Eyjafjorour fjord and frozen lakes, Sandra - who is from Stuttgart, Germany, but has lived in Iceland since the 1990s - asks who our favourite characters are. She then offers interesting theories about plot mysteries and regales us with trivia.
"Most of the shooting locations are just by the side of the road," she says, pointing out a rock-strewn area and then calling up the scene it featured in on her iPad.
"Why? In winter, you don't want to lug tonnes of camera equipment on foot. Besides, it doesn't look very much different if you hike deeper in."
Even so, landscape "inaccuracies" irk her when she watches the show: "They're supposed to be travelling great distances, but you keep seeing them pass the same rocks."
Our route takes us past Ljosavatn, or Lake of the Light, home region of Icelandic lawspeaker and pagan priest Thorgeir Thorkelsson, who decided in the year 999 that Iceland would convert to Christianity, thereby easing pressure from the Norwegian king and averting civil conflict.
History comes alive
The religious transition was achieved peacefully, with his three caveats: that Icelanders be allowed to still worship the old Norse gods, eat horse meat and abandon their babies in the wild.
Game Of Thrones fans would see parallels with Icelandic history: the uneasy truce between the Old Gods-worshipping northerners and the New Gods-following power brokers in King's Landing in the south; and the discrimination against the baby-sacrificing wildlings beyond The Wall - a fortification of solid ice on the border of the Seven Kingdoms in the book.
We stop at Godafoss, Waterfall of the Gods, into which Thorgeir cast his pagan idols to symbolise the change. Icicles fringed the falls, its thundering considerable even from a distance.
From there, we drive along the River Laxa, dodging grey geese on the road, to the pseudo-craters on the shores of Lake Myvatn. Formed by steam explosions when water is heated in lava, these pseudo-craters or rootless cones look like the real deal, except that they have no access to magma underground.
Besides our hike at Lake Myvatn, we also take a walk through Dimmuborgir (Icelandic for "dog city"), where scenes of wildling leader Mance Rayder's base were filmed.
The nature reserve is filled with stacks of lava rock, dating back 2,500 years, said to be petrified trolls (again).
Solveig leads us down one of the narrow paths to show us the profile of the squirrel in one of these rock towers. Sandra points out a bunch of stone "ladies" waiting in line, as though for the bathroom. Dimmuborgir is also said to be the home of the 13 Yule Lads, Icelandic versions of Santa Claus.
Lunch is at Vogafjos Cafe, literally a cowshed with a restaurant attached, which Sandra says was a favourite of the HBO crew when they were there for three weeks in November 2012.
After an excellent dish of pan-fried arctic char (about 4,000 kroners), I visit the patiently dozing cows next door.
A pit stop followed at the "love cave", where Jon Snow and Ygritte frolicked after entering through the rocks we had previously seen on Lake Myvatn.
Unfortunately, it is too icy and slippery to venture in. In any case, the waters, at 40 deg C, are too hot to bathe in (the actual love scene was shot in a studio).
Then, it is on to the "stinky mudpots" at Hverir at the base of the volcanic Namafjall (Mining Mountain), which, mercifully, does not reek so much of sulphur on this particular day. The mud is acidic and not to be touched.
Our final stop, the Myvatn Nature Baths, is where I sit up to my neck in geo-thermal waters while watching snow flurries - before screaming as I run through the cold back into the changing room.
On our drive back to Akureyri, Sandra asks: "Were you expecting the Wall?"
The Wall in the TV series is a CGI- enhanced version of a real glacier in south Iceland.
"This tour requires a lot of imagination," she adds, before offering to put on the Game Of Thrones soundtrack in the car.
I respectfully decline. The perilous beauty of the Icelandic north is drama enough.