Although buildings like the one shown in 1 were technically possible, it was considered to be impractical and not built until people like 2 invented and perfected X. Identify 2 and tell us what is X.

1. 2.

Cracked by: Raghuvansh , Prasad , Kal , AmK , Dibyo , p vs np , Martin , username , udupendra , Rohan , Debasish , nisha’s thambi , karthik , sumo_ftb , Ananth , Aparna , duriel , Jo , darksideofchand , Pawankumar Hegde , Ps and sidsen.

Raghuvansh, Prasad, Kal, AmK, Dibyo, p vs np, Martin, username, udupendra, Rohan, Debasish, nisha’s thambi, karthik, sumo_ftb, Ananth, Aparna, duriel, Jo, darksideofchand, Pawankumar Hegde, Ps and sidsen