Why no te with tātahi?

[[k:tātahi]] (“the beach / the seashore”) is a common place word that is used without te in location phrases: Kei tātahi …

Rule of thumb:

• For most place nouns, use Kei te + place: Kei te kura / Kei te marae.
• For tātahi (and some fixed place words like tāwāhi “overseas”), you’ll hear the form Kei tātahi (no te).