Blowing hot and cold: Iceland

As I slowly inched towards the cliff's edge, daring myself to peer down to the fast-flowing river six metres below, my 13-year-old daughter darted past me, leaping in. With a piercing scream and arms flailing, Emelye plunged into the icy water. My heart stopped, waiting for her to surface. When she did, I held my breath as she frantically swam towards a couple of tour guides standing on the riverbank with their arms outstretched, ready to haul her out before she was swept downstream.

"So who's next?" our tour leader asked.

I didn't realise we were expected to jump off a cliff when I'd signed up for this half-day river-rafting trip from Reykjavik, Iceland's capital city. I brought Emelye and my 11-year-old son Luke to Iceland because we wanted an active holiday - something more exciting than a summer spent lying by a pool - but for me, leaping into a freezing cold river was never part of the deal.

However, Luke was game and so was my husband, although he squealed louder than our daughter before slamming into the water. For them, the cliff jump - and the fact that our young, enthusiastic guides from Arctic Adventures had deliberately capsized our rafts - turned what might have been a tame trip along the Hvítá River into a highlight of our holiday.

"Am I going to die, Mummy?" Luke asked on the third day of our trip, when I explained that we were going to descend 122 metres into the heart of a sleeping volcano. As Thrihnukagigur is the only volcano in the world where you can enter the magma chamber, this was to be a once-in-a-lifetime experience. At least, that's what I told Luke.

"What if it erupts while we're down there?" he asked. It was a good question, especially because Iceland is one of the most active volcanic regions in the world. But I figured since this volcano had been dormant for 4,000 years, it would take a rather extreme case of bad luck for it to spring to life while we were inside.

Our "journey towards the centre of the earth"- as the tour company described it - started at a desolate car park in Blue Mountains Country Park, a 20-minute drive from Reykjavik. From there we were led on a 3km trek across a lava field to the crater. Any doubts I had that this might not be a child-friendly trip seemed laughable when we were joined by American actress Jennifer Connelly and her British actor hubby Paul Bettany, with their 15-month-old toddler and eight-year-old son in tow. They were in Iceland for the filming of Noah.

At a prefab hut close to the crater, we were handed our safety gear - harnesses and helmets - then led up a short, steep slope and over a narrow metal footbridge that stretched across the jagged mouth of the volcano, below which sat an open-topped cage that looked suspiciously like one of those contraptions window cleaners use to go up and down skyscrapers. Gingerly, we climbed in and were lowered into the magma chamber.

Tall enough to swallow the Statue of Liberty and wide enough to fit three basketball courts, the floor and walls of the chamber were lined with vivid ruby red, amber and purple rocks, lit by strategically placed halogen lights. Scrambling over boulders and gazing up at the sky through the pinprick opening above was an undeniably unique, oddly spiritual experience for me, but the children were underwhelmed. "It's amazing," Emelye said. "What's for lunch?"

She preferred our horse ride across a lava field in the shadow of the Eyjafjallajökull volcano, which erupted in 2010. A heavy fog meant we weren't able to enjoy the views, but the gentle nature of the Icelandic horses meant that Emelye and Luke, both novice riders, were able to trot along independently.

We also took a guided walk on along the Mýrdalsjökull glacier, still smothered with black ash from Eyjafjallajökull's eruption. With crampons slipped over our trainers, it was easy to climb the blue-white tongue of ice, but again the fog blanketed our view. The children had fun hacking at icy blocks with their hand picks, though.

I was relieved the weather was clear for our whale-watching excursion, when we were lucky enough to spot a minke whale swimming about five to 10 metres from the boat. There's no need to prebook a cruise, even in the height of summer - we just turned up at Reykjavik's Old Harbour and jumped on the next boat.

The children moaned "boooring" to my suggestion of a day trip from Reykjavik to the Golden Circle. The looping route includes Gullfoss (Golden Falls), Strokkur geyser and Þingvellir (Thingvellir) National Park, the site of Iceland's ancient parliament and where you can see the American and Eurasian tectonic plates pulling apart, albeit at a few millimetres a year. But even Luke was wowed by the thundering falls, and we were all mesmerised by Strokkur, which obligingly belched water 9.1 metres into the air several times in 30 minutes. At the Blue Lagoon, the most famous of Iceland's many geothermal spas, we spent an afternoon in the milky warm water until our fingers and toes were wrinkly, smearing our faces in white silica mud and drinking fruit juices and beers from the swim-up bar.

The only downside to Iceland is that it is ruinously expensive. Before the end of our holiday we had maxed out our credit cards, so we spent the last couple of days doing the cheap things in Reykjavik: cycling around the compact city centre and swimming in its thermally heated pools.

Fortunately, the city is made for exploring by bike. With a population of just 120,000, it feels like a small town, and a network of cycle paths makes it one of the safest cities in the world to be on two wheels.

We whizzed along the seafront to the Old Harbour, where we stopped at the Kolaportio weekend flea market and tried shark's meat, which tasted as bad as it smelled. However, the hot dogs from Bæjarins Beztu, a hut in a city centre car park, were delicious.

We weaved our way up steep, quiet streets lined with pastel-coloured houses and arty boutiques to reach the city's tallest building, the rocket-shaped Hallgrímskirkja Lutheran Church, which soars over the rooftops. When we returned to the seafront at 10pm, the sun was just dipping below the horizon.

On our last day, we swam in the deliciously warm and chemical-free Laugardalslaug outdoor pool, the largest in Iceland, and relaxed in hot pots heated by the volcanoes bubbling below the earth's crust, while the children enjoyed Laugardalslaug's water chute about a zillion times. "Going inside a volcano was good," Luke said, "but this is way more fun".

FACT BOX

The art deco-style Hótel Borg in the centre of Reykjavik is one of the city's coolest hotels. Doubles cost from about 250 euros (HK$2,544). www.hotelborg.is

Many of the activities described can be booked via Arctic Adventures. Its Full Throttle tour, which combines a quad bike (ATV) tour and river rafting, costs 28,990 Iceland krona (HK$1,927), including lunch and pickup in Reykjavik. www.adventures.is

Horse-riding and glacier walks can be booked year-round via Eldhestar. A day trip, combining a horse ride with a glacier walk, plus lunch, costs US$250 per person. www.eldhestar.is

Inside the Volcano is taking trips into Thrihnukagigur until September 10, for 30,000 Iceland krona per person for five hours, including the trek to the crater. www.insidethevolcano.com

Entry to the Blue Lagoon costs from 33 euros. www.bluelagoon.com

Whale-watching cruises with Elding start from 8,000 Iceland krona for two-and-a-half to three hours. www.whalewatching.is