The Galactic archeology is trying to understand the formation history of the Milky Way. To study the early Milky Way history one can use old population stars that carry information about their past in their current dynamical and chemical properties, which makes them invaluable in studies of the Milky Way formation history. In my research, I use old (< 10 Gyr) variable stars of the RR Lyrae class, which serve as standard candles and tracers of metallicity within the Local Group. In my talk, I will discuss their use for studying the northern stellar overdensity near the Small Magellanic Cloud (SMCNOD) together with their spatial and kinematical distribution in the Galactic bulge and Galactic disk. I will also address some of the open questions related to RR Lyrae variables, like the Oosterhoff dichotomy and the uncertainty in their mass due to the lack of RR Lyrae stars in binary systems.