Question: What attraction, located on Heart Island, was built by the G. W. & W. D. Hewitt architectural firm?

Context articles: Gummer and Ford
G. W. &amp; W. D. Hewitt
Harold W. Burton
Bohlen, Meyer, Gibson and Associates
ZGF Architects LLP
C. F. Møller Architects
Drexel Development Historic District
Architectural firm
Tachau and Vought
Boldt Castle

Gummer and Ford was an architectural firm founded in 1923 in Auckland, New Zealand by William Henry Gummer and Charles Reginald Ford.
 It was among the country's best-regarded architectural firm of the first half of the 20th century, designing numerous iconic buildings, including the former National Art Gallery and Dominion Museum in Wellington and the old Auckland Railway Station.
 Eighteen of the company's buildings have been registered as significant historic places by Heritage New Zealand.
 In 2006 an exhibition of their work was staged at The University of Auckland's Gus Fisher Gallery, and in 2007 the firm was described as 'the best architectural practice of all time in New Zealand'.
G. W. & W. D. Hewitt was a prominent architectural firm in the eastern United States at the turn of the twentieth century.
 It was founded in Philadelphia in 1878, by brothers George Wattson Hewitt (1841–1916) and William Dempster Hewitt (1847–1924), both members of the American Institute of Architects.
 The firm specialized in churches, hotels and palatial residences, especially crenelated mansions such as Maybrook (1881), Druim Moir (1885–86) and Boldt Castle (1900–04).
 The last was built for George C. Boldt, owner of Philadelphia's Bellevue-Stratford Hotel (1902–04), G.W. & W.D. Hewitt's most well-known building.
Harold William Burton (October 23, 1887 – October 2, 1969) was an early 20th-century architect with architectural works throughout the western United States and Canada.
 Burton was one of the most prolific architects of chapels, meetinghouses, tabernacles and temples for The Church of Jesus Christ of Latter-day Saints (LDS Church).
 In 1910 he opened an architectural firm with Hyrum Pope (Pope and Burton) in Salt Lake City, Utah.
 They were particularly fond of Frank Lloyd Wright and the Prairie School architectural style.
 As young architects, Pope & Burton won design competitions for two of their better-known works, the Cardston Alberta and Laie Hawaii temples of the LDS Church.
 Burton moved to Los Angeles, California in 1927 to set up another office in the firm with Pope.
 After Pope unexpectedly died in 1939, Burton established a new firm with his son Douglas W. Burton.
 Together they continued to design many buildings, including some for the church.
 In 1955, Harold became the chief supervising architect for the LDS Church.
 One of his final works was the Oakland California Temple.
 Aside from places of worship, Burton also designed civic buildings and homes.
 Many of his works exist today, some of which are listed on the National Register of Historic Places.
Bohlen, Meyer, Gibson and Associates, or BMG, is an architectural firm based in Indianapolis, Indiana.
 It was founded in Indianapolis on April 10, 1853, as D. A. Bohlen, Architect by Diedrich A. Bohlen, German immigrant.
 In 1884, after Diedrich's son, Oscar D. Bohlen, joined the firm it was renamed D. A. Bohlen and Son.
 Four successive generations of Bohlen architects have worked at the firm: Diedrich A. Bohlen (its founder), Oscar D. Bohlen (Diedrich's son), August C. Bohlen (Diedrich's grandson), and Robert L. Bohlen (Diedrich's great-grandson).
 The firm specialized in institutional projects, especially civic, religious, and educational buildings.
 In 1971 Melvin B. G. Meyer acquired majority interest in the firm, which adopted its name in reference to its founder and its two principal architects, Meyer and John M. Gibson.
 The architectural firm is among the oldest still operating in the United States.
 More than twenty of its projects are listed on the National Register of Historic Places.
ZGF Architects LLP (ZGF), formerly Zimmer Gunsul Frasca Partnership, is an American architectural firm with offices in Portland, Oregon; Seattle, Washington; Los Angeles, California; Washington D.C.; New York, New York; and Vancouver, Canada.
 Founded in 1942, the firm was listed in 2011 as the #4 architectural firm in the United States by "Building Design+Construction", and ranked the #9 architectural firm by "Architect".
 In 2016 "Architect" named ZGF the #1 architecture firm in the country, citing the organization's dedication to sustainability as a major deciding factor.
 Between the company's five offices in the United States and their office in Canada they employ more than 600 employees.
Arkitektfirmaet C. F. Møller, internationally also known as C. F. Møller Architects, is an architectural firm based in Århus, Denmark.
 Founded in 1924 by C. F. Møller, it is today the largest architectural firm in Denmark based on number of employed architects.
 About half the revenue is earned outside Denmark.
 Besides the main office in Århus, the firm has offices in Copenhagen, Oslo, London and in 2007 it bought the Stockholm-based Swedish architectural practice Berg Arkitekter which is still operated under its own name.
Drexel Development Historic District is a national historic district located in the University City neighborhood of Philadelphia, Pennsylvania.
 It encompasses 96 contributing rowhouses dated to the mid- to late-19th century.
 A number of the rowhouses were designed by noted architect Samuel Sloan.
 The architectural firm G. W. & W. D. Hewitt designed rowhouses for developer Anthony Joseph Drexel on the block bounded by Pine, new 39th, Baltimore, and 40th Streets.
 They are representative of a number of popular architectural styles including Second Empire, Italianate, and High Victorian.
In the United States, an architectural firm or architecture firm is a company which employs one or more licensed architects and practices the profession of architecture; while in other countries such as the United Kingdom, an architectural firm is a company which offers architectural services.
Tachau and Vought was an American architectural firm active in the mid-twentieth-century New York City that specialized in mental hygiene hospitals.
 It was established in 1919 as the successor to the architectural firm of Pilcher and Tachau by William G. Tachau (b. 1875) and Vought.
 By 1946, Vought had left.
 Eliot Butler Willauer (April 4, 1912 – February 6, 1972) was a principal from around 1945 until 1946.
 The firm moved from 109 Lexington Avenue to 102 East 30th Street around 1923.
Boldt Castle is a major landmark and tourist attraction in the Thousand Islands region of the U.S. state of New York.
 Open to guests seasonally between mid May and mid October.
 It is located on Heart Island in the Saint Lawrence River.
 Heart Island is part of the Town of Alexandria, in Jefferson County.
 Originally a private mansion built by an American millionaire, George Boldt, it is today maintained by the Thousand Islands Bridge Authority as a tourist attraction.