A dual firing line drilling installation for drilling a well, for example an oil, a gas, or a thermal well, by means of said installation, which installation comprises: - a drilling tower main structure having four frameworks (3, 5, 7, 9) that are each over a major portion of their height U-shaped in horizontal cross-section, so that each of said frameworks has an opened vertical side (13, 15, 17, 19), wherein a four-sided central space is present in the tower, and wherein along each side of the central space one of said four frameworks is arranged with its opened vertical side facing the central space, the frameworks being interconnected to form said drilling tower main structure, - a first storage device for vertically storing drilling tubulars, said first storage device being housed in a first framework of the drilling tower main structure; - a second storage device for vertically storing drilling tubulars, said second storage device being housed in a second framework of the drilling tower main structure which is located generally opposite from the first framework of the drilling tower main structure, - a first hoisting device supported by a third framework of the drilling tower main structure, which first hoisting device is adapted to manipulate a string of drilling tubulars in a first firing line extending vertically within said third framework; - a second hoisting device supported by a fourth framework of the drilling tower main structure, which fourth framework is located generally opposite from the third framework of the drilling tower main structure, and which second hoisting device is adapted to manipulate a string of drilling tubulars in a second firing line extending vertically within said fourth framework; - a first pipe racker housed within the drilling tower main structure and adapted to move drilling tubulars while supported in vertical orientation between at least one of the storage devices and at least the first firing line via said opened vertical sides of the respective frameworks; - a second pipe racker housed within the drilling tower main structure and adapted to move drilling tubulars while supported in vertical orientation between at least the second storage device and at least the second firing line via said opened vertical sides of the respective frameworks. - a drilling tower main structure having four frameworks (3, 5, 7, 9) that are each over a major portion of their height U-shaped in horizontal cross-section, so that each of said frameworks has an opened vertical side (13, 15, 17, 19), wherein a four-sided central space is present in the tower, and wherein along each side of the central space one of said four frameworks is arranged with its opened vertical side facing the central space, the frameworks being interconnected to form said drilling tower main structure, - a first storage device for vertically storing drilling tubulars, said first storage device being housed in a first framework of the drilling tower main structure; - a second storage device for vertically storing drilling tubulars, said second storage device being housed in a second framework of the drilling tower main structure which is located generally opposite from the first framework of the drilling tower main structure, - a first hoisting device supported by a third framework of the drilling tower main structure, which first hoisting device is adapted to manipulate a string of drilling tubulars in a first firing line extending vertically within said third framework; - a second hoisting device supported by a fourth framework of the drilling tower main structure, which fourth framework is located generally opposite from the third framework of the drilling tower main structure, and which second hoisting device is adapted to manipulate a string of drilling tubulars in a second firing line extending vertically within said fourth framework; - a first pipe racker housed within the drilling tower main structure and adapted to move drilling tubulars while supported in vertical orientation between at least one of the storage devices and at least the first firing line via said opened vertical sides of the respective frameworks; - a second pipe racker housed within the drilling tower main structure and adapted to move drilling tubulars while supported in vertical orientation between at least the second storage device and at least the second firing line via said opened vertical sides of the respective frameworks.