Questions & Answers about Idę na spacer mimo deszczu.
With motion towards an activity or event, Polish typically uses na + Accusative. Spacer (a walk) is treated like an activity, so you say iść na spacer, similar to:
- iść na koncert (go to a concert)
- iść na obiad (go for lunch)
- iść na siłownię (go to the gym)
Using do would suggest going into a concrete place (e.g., do szkoły, do domu), not into an activity.