The magazine's sustainability editor Juliet Kinsman celebrates the ten destinations in an article on the magazine's website for "setting new benchmarks, spotlighting specific environmental issues and helping to make the world a better place for people and planet".
Under a picture of Bled Island, Kinsman describes Slovenia as a compact Central European country with "chocolate-box mountain scenery and medieval fairy-tale villages, which "punches above its weight in the conservation stakes".
The editor has been taken by Slovenia's "walkable, welcoming capital" Ljubljana, which she says has long been a hit for eco-minded city breaks.
The article notes that more than a tenth of Slovenia's rolling countryside is formally protected, "spanning Alpine peaks, ancient forests, Karst plateau, the Pannonian plains' vineyards and thermal waters and the 29-mile stretch of Adriatic coast".
Visitors are advised to consult the Slovenian Tourist Board's (STO) Green Scheme of Slovenian Tourism, a national and certification programme that has been systematically promoting sustainable models in tourism for six years, the STO said.
Apart from Slovenia, the other ten Conde Nast Traveller sustainable destinations to visit in 2021, which are listed in no particular order, are Costa Rica, Finland, Greece, Scotland, Palau, Malawi, Portugal, Hawaii and Bhutan.
The STO notes that Slovenia has recently attracted the attention of many esteemed global travel and other media. On Sunday, The Sun placed Slovenia second in its pick of travel destinations when those are made possible again, where sustainability plays a major part.
In October, Slovenia made the Forbes list of 20 destinations to visit in 2021 and the Lonely Planet included Bled on its Ultimate Travel List after Conde Nast Traveller made Slovenia its top travel destination for 2021 in September last year.
The Financial Times and The Guardian have also recommended Slovenia as their top travel destinations for 2021, and the Lonely Planet has recently listed Ljubljana as one of the world's eight most sustainable cities.