A telescoping substructure of a drilling rig, the telescoping substructure comprising: first and second laterally spaced-apart telescoping substructure boxes (110, 120), each comprising: a lower substructure box (110L, 120L); an upper substructure box (110u, 120u) that is adapted to be telescopically raised and lowered relative to said lower substructure box (110L, 120L); and raising means for telescopically raising and lowering said upper substructure box (110u, 120u) relative to said lower substructure box (110L, 120L) between a collapsed configuration for transportation and a raised configuration for drilling operations, and characterised in that said upper substructure box (110u, 120u) comprises a plurality of structural members (111c/e/h, 112e/h, 113c/e/v) that are assembled to define a substantially open interior space and a substantially open bottom frame, wherein said substantially open interior space is sized to receive at least a portion of said lower substructure box (110L, 120L) through said substantially open bottom frame when said upper substructure box (110u, 120u) is telescopically raised and lowered relative to said lower substructure box (110L, 120L), and wherein each of said first and second telescoping substructure boxes (110, 120) are adapted to facilitate a horizontal movement of said telescoping substructure across ground adjacent to a wellbore location in at least one of a lateral direction and a longitudinal direction over wellhead equipment positioned above said wellbore location while said upper substructure boxes (110u, 120u) are in said raised configuration, said lateral direction being substantially perpendicular to each of said first and second telescoping substructure boxes (110, 120) and said longitudinal direction being substantially parallel to each of said first and second telescoping substructure boxes (110, 120). a lower substructure box (110L, 120L); an upper substructure box (110u, 120u) that is adapted to be telescopically raised and lowered relative to said lower substructure box (110L, 120L); and raising means for telescopically raising and lowering said upper substructure box (110u, 120u) relative to said lower substructure box (110L, 120L) between a collapsed configuration for transportation and a raised configuration for drilling operations, and characterised in that said upper substructure box (110u, 120u) comprises a plurality of structural members (111c/e/h, 112e/h, 113c/e/v) that are assembled to define a substantially open interior space and a substantially open bottom frame, wherein said substantially open interior space is sized to receive at least a portion of said lower substructure box (110L, 120L) through said substantially open bottom frame when said upper substructure box (110u, 120u) is telescopically raised and lowered relative to said lower substructure box (110L, 120L), and wherein each of said first and second telescoping substructure boxes (110, 120) are adapted to facilitate a horizontal movement of said telescoping substructure across ground adjacent to a wellbore location in at least one of a lateral direction and a longitudinal direction over wellhead equipment positioned above said wellbore location while said upper substructure boxes (110u, 120u) are in said raised configuration, said lateral direction being substantially perpendicular to each of said first and second telescoping substructure boxes (110, 120) and said longitudinal direction being substantially parallel to each of said first and second telescoping substructure boxes (110, 120).