This in the dative singular (þessum, þessari, þessu)

When describing a location, prepositions like í (in), á (on/at), hjá (next to), and frá (from) trigger the dative case.

To say "this" specific place, the demonstrative pronoun þessi (this) changes to match the noun's gender in the dative.

Gender"This" (Dative)
Masculineþessum
Feminineþessari
Neuterþessu

Grammar tip: After a demonstrative pronoun, the noun drops its definite article (like *-inn, -in, or -ið) and uses its indefinite dative form.*

Feminine Locations

For feminine nouns like gata (street) and bygging (building), use þessari.

I live on this street.
Ég bý á þessari götu.
She works in this building but not in the train station.
Hún vinnur í þessari byggingu en ekki í lestarstöðinni.

Masculine Locations

For masculine nouns like banki (bank) and turn (tower), use þessum.

There is no one in this bank.
Það er enginn í þessum banka.
Today I am going to work in this tower.
Í dag ætla ég að vinna í þessum turni.

Neuter Locations

For neuter nouns like torg (square) and safn (museum), use þessu.

You find the museum on this square.
Þú finnur safnið á þessu torgi.
Usually they meet us at this museum.
Venjulega hitta þeir okkur á þessu safni.