Traveller for the construction of engineering works, comprising: - a securing structure for securing to the already built engineering work; - a working structure on which construction of the work advances; characterized in that: - the securing structure comprises: - a first end ring coupled to the perimeter of the section of the already built work; - a second middle ring coupled to the perimeter of the section of the already built work; - at least one transversal cross-brace that joins the end ring and the middle ring on a side of the traveller; - connecting elements between the end ring and the middle ring; - the rings (6, 7) are joined at the upper part thereof by an upper cross-brace framework and at the lower part thereof by at least one main load-bearing girder (10,10') and a bar framework; - the upper cross-brace framework comprises two vertical posts in the upper cross-braces corresponding to the end ring and two vertical posts in the upper cross-braces corresponding to the middle ring; - a sliding bar passes through the inside of each one of the two vertical posts corresponding to the middle ring; - the working structure comprises: - an exterior formwork; and - a floor formwork; wherein the securing structure and the working structure are joined at the lower part thereof by said main load-bearing girder (10, 10') and at the upper part thereof by forward tracks (18, 18') supportingly connectable with said vertical posts (12,12'). - a securing structure for securing to the already built engineering work; - a working structure on which construction of the work advances; characterized in that: - the securing structure comprises: - a first end ring coupled to the perimeter of the section of the already built work; - a second middle ring coupled to the perimeter of the section of the already built work; - at least one transversal cross-brace that joins the end ring and the middle ring on a side of the traveller; - connecting elements between the end ring and the middle ring; - the rings (6, 7) are joined at the upper part thereof by an upper cross-brace framework and at the lower part thereof by at least one main load-bearing girder (10,10') and a bar framework; - the upper cross-brace framework comprises two vertical posts in the upper cross-braces corresponding to the end ring and two vertical posts in the upper cross-braces corresponding to the middle ring; - a sliding bar passes through the inside of each one of the two vertical posts corresponding to the middle ring; - the working structure comprises: - an exterior formwork; and - a floor formwork; - the securing structure comprises: - a first end ring coupled to the perimeter of the section of the already built work; - a second middle ring coupled to the perimeter of the section of the already built work; - at least one transversal cross-brace that joins the end ring and the middle ring on a side of the traveller; - connecting elements between the end ring and the middle ring; - the rings (6, 7) are joined at the upper part thereof by an upper cross-brace framework and at the lower part thereof by at least one main load-bearing girder (10,10') and a bar framework; - the upper cross-brace framework comprises two vertical posts in the upper cross-braces corresponding to the end ring and two vertical posts in the upper cross-braces corresponding to the middle ring; - a sliding bar passes through the inside of each one of the two vertical posts corresponding to the middle ring; - the working structure comprises: - an exterior formwork; and - a floor formwork; - an exterior formwork; and - a floor formwork;