Normally, you'll have to complete the troublesome Golden Ticket side quest if you want to find Koller's Workshop. However, there's an alternate method. In Prague, after reaching the plaza located between the stone archways (look for a large boulder suspended overhead), jump to the top of the arch positioned above the checkpoint. You'll need to climb the scissor lift nearby in order to make the leap. Next, jump across the window sills and follow the rooftops until you arrive at the balcony attached to a pink apartment building. Access that balcony and enter the building, then climb through the ventilation ducts. You'll make your way to the rooftops, so that now you're positioned over the Time Machine bookstore. Proceed across the next archway and stick to the right as you follow window sills and ledges. When you can reach the single-story warehouse, jump to it. With the cloaking aug active, drop into the warehouse and proceed to the locker room near the back. Now climb into the vents, breaking a vent cover positioned to your right. Follow that duct and you'll finally reach the elevator that grants access to the workshop.