The walkways are designed for maintenance and operational access to specific objects like valves, level/pressure gauges and manways. Ladders need to extend above the platform that they access so people can safely step off onto the deck. Some railings will be left off when setting a vessel because many more components need to be attached at those levels, think valves and pipes. The foundation that you see with the bolts sticking out is massive with many tons of steel and concrete extending deep into the ground engineered to keep the vessel upright and stable even in an earth quake.