CREATE TABLE table_203_28 (id DECIMAL, "year" DECIMAL, "competition" TEXT, "venue" TEXT, "position" TEXT, "event" TEXT, "notes" TEXT)

where was the only 5km event held ?
SELECT "venue" FROM table_203_28 WHERE "event" = '5 km'
SELECT "venue" FROM "table_203_28" WHERE "event" = '5 km'