<div class="1">
<div class="2">
</div>
</div>
.1{ position: relative;
width: 200px;
height: 200px;
}
.2 {position: absolute;
height: 100%;
width: 100%;
top: 0px;
left: 0px;
opacity: 0;
}
.2.active{ opacity: 1 }
<div class="changeable">
<div id="block-1" class="block visible">Первый</div>
<div id="block-2" class="block">Второй</div>
</div>
div.block {
display: none;
}
div.block.visible {
display: block;
}
$('.block').on('click', function(){
$(this).closest('.changeable').find('.block').toggleClass('visible');
});