Polish alpinist Darek Sokołowski has established the world's second D16 dry-tool line at the steep and imposing Capanna Bill, or 'Tomorrow's World' cave in the Italian Dolomites, with an ascent of Parallel World, an extension of his unrepeated 2017 route War Without End D15+. Sokołowski opted to climb in pure Dry-Tooling Style, avoiding the use of fig-fours in order to increase the physical difficulty.

Parallel World is only the third route to be given a rating of D16, after Gordon McArthur's 80 metre-long Storm Giant in British Columbia, Canada (UKC news report) and Oświecenie in Zakopane, Poland. Tom Ballard's A Line Above the Sky D15 (UKC news report), also located in the Tomorrow's World cave, was previously the world's hardest dry-tool route.

According to a report by Rock and Ice, Sokołowski spent 50 minutes climbing the 60-plus metre line, which includes 12 metres of stepped overhangs and a 50 metre near-horizontal roof. The crux is situated at the end of the route, which features long, powerful moves and no rests leading up to this point.

Aside from establishing War Without End D15+ and now Parallel World D16, Sokołowski has repeated many of the hardest neighbouring climbs at Tomorrow's World: Je Ne Sais Quoi D14+, Oblivion D14, A Line Above The Sky D15-, all in Dry-Tooling Style.