Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_45506 ( "Pinnacle height" text, "Year" real, "Structure type" text, "Main use" text, "Country" text, "Town" text )

### Question ###
What is the main use for the structure listed in walker city, iowa?

### Accurate SQL ###

SELECT "Main use" FROM table_45506 WHERE "Town" = 'walker city, iowa'