One of the biggest attractons in Tilcara is El Pucará, a ruined fortification from the Inka era. In some places at the site, they have reconstructed the houses to their supposedly originally appearance. This is possibly why these ruins are so popular. Personally I think the ruins in Quilmes and Tastil are better sights. For these ruins there is no entrance fee, whereas in Tilcara you have to pay. But it could be that I had a saturation of pre-Colombian ruins when I came to Tilcara.