The vast Shahdag National Park covers over 1.3 million sq km, encompassing many of the nation's most spectacular peaks and high-mountain trails. Lower areas of the park can be entered with a standard national park entrance ticket that must be prepurchased (online or via bank transfer). However, some of the most appealing areas are considered 'border zones' and subject to very awkward regulations that can take several weeks of preparation to fulfill.
Behind Laza and Xınalıq, a roadless crag-framed valley sweeps around to provide access to the base camps for some splendid 4000m-plus Caucasian peaks seemingly ripe for relatively nontechnical climbs. Best known are glacier crowned Şahdağ (4243m, three days), tough scree-plagued Bazarduzu Dağ (4466m, four days) and impressively pyramidal Tufandağ (4100m, three days).
However, there are two huge bureaucratic 'buts'. Firstly the national park entrance ticket must be prepurchased (online), but standard tickets only apply to certain southern and western areas of the park. The bits you're most likely to want to see require a special high mountains ticket AND a special 'border zone' pass from the military authorities. Such passes have for years been essentially unavailable, and soldiers might aggressively stop anyone walking unsanctioned even 100m into national park territory, meaning that few have visited Azerbaijan's top outdoor highlights in recent years.
However, as of 2015–16, things appear to have relaxed just an iota for those prepared to send off documents around three weeks in advance and to employ an officially sanctioned guide such as Mevlud Azizov. Alternatively ask Shahdag Mountain Tours about its (pricey) mountaineering packages: they're brand new and evolving but still require serious advance planning.
For alternative 'free' treks, explore the villages outside the park and perhaps make the multi-day crossing from Qarxun to Lahic via Babadağ.