To some, this meteor crater north of Pretoria is a holy place. To Janine Stephen, it's a great day trip

EXTREME heat can do odd things to the horizon, but this is no mirage. Stumble over the sultry lip of the Tswaing Meteorite Crater and there, reflecting enormous skies, is the most peculiar-looking lake this side of dreamland. An electric blue-green in high summer, it broods and bubbles in eerie silence - the crater walls cut off both breezes and sounds from the outside world. It's like a gigantic witchy cauldron, just waiting to cook an unwary traveller.

The unearthly depression was punched into the soils just north of Pretoria some 220000 years ago, back when long-horned giant buffalo still cruised the grasslands and modern humans, Tuscan-themed suburbs and bustling townships were kind of scarce. Simon Nyalungu, a guide with encyclopaedic knowledge of the crater, says that on that fateful day, a stony meteor, anywhere from 30 to 50m across, came barrelling out of the heavens and thwacked into Earth with the force of 100 atom bombs. The resulting crater - just about circular, surprisingly peaceful - is one of 170 found on Earth - and the salty lake within makes it even rarer.

Ever since the cataclysm, locals rated Tswaing as an unusual place. There were early Stone-Age people living in the Wonderboompoort area who could have seen the roar and blaze of the event itself, which should have kick-started some interesting oral history.

Later, Iron-Age folk would trek to the lake - up to seven times saltier than sea water - to collect salt. "Only women were allowed to collect the salt deposits," Nyalungu says. To keep the children away and prevent pollution of the precious resource, they circulated stories about a huge serpent living beneath the water.

In about the mid-1800s, the Boers proclaimed a farm named Zoutpan and proceeded to mine soda ash and salt here until about 1950. Sediment was hauled by ox-wagon to the factory, the scanty remains of which can be seen nearby. The crater's next incarnation was an experimental cattle farm.

It was only after 1990 that Tswaing's rarity was fully acknowledged. For decades, a hot topic in geologist circles was whether Tswaing was just your average, garden-variety volcanic crater or not. The debate was finally put to rest after a drill core showed up tell-tale glass sediments that could only have been formed by an impact explosion. Tswaing was handed over to museum authorities in 1992 and the site is now managed by Ditsong Museums. The crater itself is surrounded by 2000ha of nature reserve and it's now a top Gauteng birding site.

A delicate footpath snakes around the crater, from the rim right down to the lake shore - part of a 7.2km trail. Navigating just the 1.3km diameter crater takes about 90 minutes, give or take plenty of time to mine Nyalungu's mother-lode of knowledge. In high summer, the air shimmers with heat and cicada screams. We picked our way down an at-times steepish path, lined with sicklebush and buffalo thorns - a branch of which can be used to collect a wandering spirit and return him or her to an ancestral home.

The lake water itself was acid green due to good rains and blooming algae. During dry months it turns the colour of Coca-Cola to match the dry-muesli tones of the surrounding bushveld. A small cross listed in the shallows along with some stilts and other waders, while candle stubs and small burnt offerings dotted an area of shore. "The crater has a lot of religious visitors, who believe it is holy," Nyalungu explains. "They say Tswaing was caused by a star that fell from space - from the heavens. Some come to take water from the lake to use in rituals, and they also collect stones." These are heated and water is poured on them to create steam - to purify believers from sins.

Goats and chickens are also sacrificed here, and snuff and beer are poured on the ground to ask for rain, because "this is a place where the ancestors listen". Some nights, Nyalungu says, you can hear groups of Zionists singing from dusk until dawn - not to be confused with the odd trance party that takes place here, where revellers kick up dust and keep an eye out for UFOs.

Tswaing has a good relationship with the surrounding community: Soshanguve and Winterveld lap around the reserve. Traditional healers in search of medicinal plants and religious visitors are given permits - only right, says Nyalungu, as they used the place long before it became a museum.

Should the funds be made available, there are plans to complete longer hiking trails - the reserve incorporates some all-too-rare wetlands and a scattering of mammals, including antelope and brown hyena. Ditsong Museums will also need to dig deep to rebuild the museum itself, which burnt down in 2009.

The site's star attraction really is the magic circle itself. Nothing like standing in its hazy silence, imagining that the soils contain traces of extra-terrestrial matter. Never mind wondering whether it could happen again. - © Janine Stephen

IF YOU GO

HOW TO GET THERE: Bypass Pretoria on the N1, heading north. Take the Wallmannsthal off-ramp, then refer to the map provided by the museum to direct you through the outskirts of Soshanguve to the entrance. It's off the M35.

NEED TO KNOW: Ravenous mosquito alert: take repellent. Entrance Is R20 for adults; guided tours start at R200. Book ahead. There's a picnic site and even group accommodation in basic chalets for R50 a night, booking essential. A copy of "Tswaing Meteorite Crater" will answer all your questions. R100 from reception.

CONTACT: 076 945 5911 (reception). See www.ditsong.org.za for more information.