520 S Mashta Dr

Key Biscayne, FL 33149

$19,900,000

$6,451/ft²

5Beds

4Baths

3,085Sq ft

1961Year built

Single-family homeType

About this home

Seize a rare opportunity to create a landmark waterfront estate on one of the largest residential lots in Key Biscayne’s exclusive Mashta Island enclave. Spanning an extraordinary 22,140 square feet, this exceptional property offers 138 feet of pristine water frontage and sweeping open water views, providing an unparalleled setting for a world class residence. Plans by renowned architect, Pablo Corazzini of Vitalini Corazzini Architects, are available to the buyer, offering a thoughtfully conceived vision that takes full advantage of the property’s remarkable scale, premier waterfront setting, and spectacular sunsets. The proposed design creates an extraordinary canvas for sophisticated indoor-outdoor living and entertaining, should the buyer choose to pursue the concept. With its exceptional lot size, expansive water frontage, and coveted Mashta Island address, this is a truly irreplaceable opportunity to create a legacy estate in one of South Florida’s most prestigious waterfront communities.

Features

Waterfront

Property details

Listing

MLS #: A12071221
Status: For sale
Listed on: Aug 12, 2026
Days on market: 15 days
Listing data updated: Aug 26, 2026

Interior

Beds: 5
Baths: 4
Living area: 3,085 ft²
Price per ft²: $6,451/ft²

Building & community

Type: Single-family home
Year built: 1961
County: Miami-Dade

Lot & exterior

Lot size: 22,140 ft²
Waterfront: Yes

Days on market, price per ft² and the monthly HOA amount are calculated by this site from the MLS data shown; the association fee is normalized to a monthly figure.

What's nearby

Elementary school: KEY BISCAYNE K-8 CENTER · 0.6 mi away
Middle school: KEY BISCAYNE K-8 CENTER · 0.6 mi away
High school: MAST ACADEMY · 3.8 mi away
Transit: CRANDON BD & W WOOD DR · 0.6 mi away
Supermarket: Winn-Dixie · 0.7 mi away
Park: Harbor Park · 0.5 mi away
Pharmacy: CVS Pharmacy · 0.6 mi away

Straight-line distances · Sources: NCES/FL DOE, GTFS Miami-Dade and Broward, OpenStreetMap

True monthly cost

Mortgage (principal & interest): $100,625
Property taxes (est.): $18,242
Home insurance (est.): $14,925
Flood insurance (est.): —

Estimated total$133,792*/mo

* Some cost lines aren't available yet for this listing; the total shown is incomplete.

Based on 20% down, a 6.5% rate and a 30-year loan, plus this home's estimated Florida carrying costs. All figures are illustrative estimates — not quotes, not financial or insurance advice.

Sources: flood zone — FEMA National Flood Hazard Layer; mortgage, taxes and insurance figures — this site's own estimates; HOA / CDD — as reported for this listing.

What will this home really cost you?