Fill a highball or tall glass with crushed or pebbled ice.
In a shaker, combine pineapple juice and coconut rum with ice. Shake until chilled.
Strain the mixture into the prepared glass over ice.
Slowly pour grenadine into the center of the drink, allowing it to settle and create a layered sunset effect.
Garnish with a fresh pineapple wedge and maraschino cherry. Serve immediately.