The number of steps built down into the interior means that it is unsuitable for the infirm or those with heart problems.
( ( ( The number ) ( of ( steps ( ( built down ) ( into ( the interior ) ) ) ) ) ) ( ( means ( that ( it ( ( is ( unsuitable ( for ( ( ( the infirm ) or ) those ) ) ) ) ( with ( heart problems ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NP (NNS steps)) (VP (VBN built) (PRT (RP down)) (PP (IN into) (NP (DT the) (NN interior))))))) (VP (VBZ means) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ is) (ADJP (JJ unsuitable) (PP (IN for) (NP (NP (DT the) (NN infirm)) (CC or) (NP (DT those))))) (PP (IN with) (NP (NN heart) (NNS problems))))))) (. .)))
It is unsuitable for those with heart issues because of the number of steps.
( It ( ( is ( unsuitable ( for ( those ( with ( ( heart issues ) ( because ( of ( ( the number ) ( of steps ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADJP (JJ unsuitable) (PP (IN for) (NP (NP (DT those)) (PP (IN with) (NP (NP (NN heart) (NNS issues)) (PP (RB because) (IN of) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS steps))))))))))) (. .)))