Over the past several months, Muscovites have been busy complaining on social media that their GPS-powered mobile apps are malfunctioning. Users of Yandex.Navigator have run into frequent problems, for example, watching their vehicles’ locations bounce all over the map. When the Pokemon Go craze arrived in Russia earlier this year, Moscow’s geolocation issues became truly widespread.

Everyone experiencing problems seems to report one thing in common: devices start going weird near the Kremlin, at the very center of Moscow. Earlier this week, the popular blogger and podcaster Grigory Bakunov, better known online as “Bobuk,” investigated these troubles firsthand .

Bakunov says he got so fed up with all the speculation about what is happening with geolocation near the Kremlin that he loaded a backpack full of devices that use GPS and GLONASS, hopped on a segway, and set off to do laps around central Moscow, measuring the strength and accuracy of his geolocation signals.

He spent three hours rolling around the Kremlin, starting at 9 a.m. and wrapping up at noon. “Cutting across the city on a segway for three hours in 2-degree weather was quite the rush,” Bakunov recalled.

The reason this stunt was more than just another vague complaint about malfunctioning geolocation is that Bakunov mapped his entire experiment. He was able to measure, in blue and red, where his GPS and GLONASS devices succumbed to location-spoofing. Take a look at his map, and you’ll see that the epicenter of the geolocation interference is somewhere inside the Kremlin.