The next primary mission is to get into a lab designated X18. When you accept the task the Barkeep will give you a Stalker Suit which will be a major improvement over the Merc Suit you've probably been wearing through Garbage and Agroprom Research Institute. Besides the better stats, the Stalker Suit also comes with nightvision which is a very nice bonus. Travel light because the Dark Valley, like many of the other areas, is likely to turn up alot of loot including artifacts and possibly a unique item or two.