Oslo

Nordmarka is not really off the beaten track in that it is accessible by T-bane and bus.
http://www.visitoslo.com/en/articles/nordmarka-forest/

Stop by the DNT office at Youngstorget 1, 0181 Oslo to find out what's happening in their outdoor world or to buy nordmarka maps.
http://english.turistforeningen.no

http://www.nytimes.com/2013/06/16/travel/36-hours-in-oslo.html

1. Just Jump

Ride Line 1 of the metro up into the forested hills northwest of the
city center to the majestic Holmenkollen Ski Jump. Skiers have been
hurtling through the air here since the 19th century, but in 2010 a
reconstructed version of the landmark was unveiled. With steel curves
reaching for the sky, the modern structure looks more like a work of
art than a sports venue. Entrance to the Ski Museum (110 kroner)
offers access to the jump tower and its 360-degree views of the city,
fjord and forests. (Holmenkollen Ski Jump and Museum, Kongeveien 5;
holmenkollen.com)

1. Norwegian Wood

Hop back on the metro heading north and alight where the line
terminates and the tranquil woods take over. This sprawling forest,
known as Nordmarka, lures adventurers year-round. In winter,
cross-country skiers stream onto nearby trails; warmer weather brings
mountain bikers and hikers. Take a brisk walk, and then retire to
Frognerseteren (Holmenkollveien 200; frognerseteren.no), a handsome
chalet with a restaurant and cafe near the metro stop of the same
name. On the terrace, sip a crisp Saison from the Norwegian craft
brewery Nogne O (half-liter, 115 kroner) and savor the spectacular
view.

Thanks, Edgar, I really appreciate your suggestions.