Hiking is extremely popular amongst Icelanders. Quite understandably. You can practically crisscross the entire country along hiking trails. Up moors and mountains, along valleys and prairies, through lava fields and fissures. And, as much as the Icelanders love their mountains, the Reykjanes Peninsula is gradually becoming the most popular area for hiking.
The Reykjanes Peninsula has excellent trails for the most experienced hikers, where you will find trails with steep climbs, trying grounds and along precipices. But, it also has excellent easy trails through areas of geological marvels. And, in most cases, the starting point is Höskuldarvellir.
Höskuldarvellir is a grassy plain (quite rare in the Reykjanes Peninsula) of 300 hectares. It is located next to Keilir, a hyaloclastite mount, quite visible from the main road between Keflavík International Airport and Reykjavík. You can park your car at Höskuldarvellir and from there you will be able to hike in any direction. You can climb Keilir which is quite steep with loose gravel, but an excellent view when you get to the top. There you will find a panoramic observation platform.
Or, you may choose to head to Trölladyngja and hike Lambafell, another hyaloclastite mount, walk through Lambafells fissure. The fissure is only a few meters across but about 50 metres deep. It is possible to hike along the entire fissure.