Japanese learning

きょうシティにいきます Instead of きょう[は]シティにいきます

Kyo city ni ikimasu.  Why there is no wa behind kyo?

Answer is really simple because kyo (today) is not the subject


I go to city today  “I” is the subject. Therefore, wa needs to go behind “I”.  

The sentence can be written:

Watashi wa kyo city ni ikimasu.


However, in real life conversation, we often omit the subject. Thus “wa” was omitted.