A landmark achievement is often refered to as reaching a Milestone!!

Milestones are constructed to provide reference points along the road. This can be used to reassure travellers that the proper path is being followed, and to indicate either distance travelled or the remaining distance to a destination. Such references are also used to by maintenance engineers and emergency services to direct them to specific points where their presence is required. This term is sometimes used to denote a location on a road even if no physical sign is present.

Olden days, there never used to be motor vehicles. Main media of reaching any place by majority people used to be by walk. Only rich people could use bullock carts or horses. Good kings were arranging to have roads for main destinations of their towns. Even on those days, distance used to be marked through milestones. Walking long distance used to be quite an adventure those days having pass through forests with wild animals, rivers etc. When people passing through these marked distance milewise, reaching next milestone was another adventure. But these days, this word of milestone is used for achieving any thing great.

Activities are tasks and milestones.

A milestone is one of a series of numbered markers placed along a road or boundary at intervals of one mile or occasionally, parts of a mile.

Destiny/goal set by us ......